CodeMirror: User Manual

Overview

CodeMirror is a code-editor component that can be embedded in Web pages. The core library provides only the editor component, no accompanying buttons, auto-completion, or other IDE functionality. It does provide a rich API on top of which such functionality can be straightforwardly implemented. See the add-ons included in the distribution, and the CodeMirror UI project, for reusable implementations of extra features.

CodeMirror works with language-specific modes. Modes are JavaScript programs that help color (and optionally indent) text written in a given language. The distribution comes with a number of modes (see the mode/ directory), and it isn't hard to write new ones for other languages.

Basic Usage

The easiest way to use CodeMirror is to simply load the script and style sheet found under lib/ in the distribution, plus a mode script from one of the mode/ directories. (See the compression helper for an easy way to combine scripts.) For example:

<script src="lib/codemirror.js"></script>
<link rel="stylesheet" href="../lib/codemirror.css">
<script src="mode/javascript/javascript.js"></script>

Having done this, an editor instance can be created like this:

var myCodeMirror = CodeMirror(document.body);

The editor will be appended to the document body, will start empty, and will use the mode that we loaded. To have more control over the new editor, a configuration object can be passed to CodeMirror as a second argument:

var myCodeMirror = CodeMirror(document.body, {
  value: "function myScript(){return 100;}\n",
  mode:  "javascript"
});

This will initialize the editor with a piece of code already in it, and explicitly tell it to use the JavaScript mode (which is useful when multiple modes are loaded). See below for a full discussion of the configuration options that CodeMirror accepts.

In cases where you don't want to append the editor to an element, and need more control over the way it is inserted, the first argument to the CodeMirror function can also be a function that, when given a DOM element, inserts it into the document somewhere. This could be used to, for example, replace a textarea with a real editor:

var myCodeMirror = CodeMirror(function(elt) {
  myTextArea.parentNode.replaceChild(elt, myTextArea);
}, {value: myTextArea.value});

However, for this use case, which is a common way to use CodeMirror, the library provides a much more powerful shortcut:

var myCodeMirror = CodeMirror.fromTextArea(myTextArea);

This will, among other things, ensure that the textarea's value is updated with the editor's contents when the form (if it is part of a form) is submitted. See the API reference for a full description of this method.

Configuration

Both the CodeMirror function and its fromTextArea method take as second (optional) argument an object containing configuration options. Any option not supplied like this will be taken from CodeMirror.defaults, an object containing the default options. You can update this object to change the defaults on your page.

Options are not checked in any way, so setting bogus option values is bound to lead to odd errors.

These are the supported options:

value (string): The starting value of the editor.
mode (string or object): The mode to use. When not given, this will default to the first mode that was loaded. It may be a string, which either simply names the mode or is a MIME type associated with the mode. Alternatively, it may be an object containing configuration options for the mode, with a name property that names the mode (for example {name: "javascript", json: true}). The demo pages for each mode contain information about what configuration parameters the mode supports. You can ask CodeMirror which modes and MIME types have been defined by inspecting the CodeMirror.modes and CodeMirror.mimeModes objects. The first maps mode names to their constructors, and the second maps MIME types to mode specs.
theme (string): The theme to style the editor with. You must make sure the CSS file defining the corresponding .cm-s-[name] styles is loaded (see the theme directory in the distribution). The default is "default", for which colors are included in codemirror.css. It is possible to use multiple theming classes at once—for example "foo bar" will assign both the cm-s-foo and the cm-s-bar classes to the editor.
indentUnit (integer): How many spaces a block (whatever that means in the edited language) should be indented. The default is 2.
smartIndent (boolean): Whether to use the context-sensitive indentation that the mode provides (or just indent the same as the line before). Defaults to true.
tabSize (integer): The width of a tab character. Defaults to 4.
indentWithTabs (boolean): Whether, when indenting, the first N*tabSize spaces should be replaced by N tabs. Default is false.
electricChars (boolean): Configures whether the editor should re-indent the current line when a character is typed that might change its proper indentation (only works if the mode supports indentation). Default is true.
rtlMoveVisually (boolean): Determines whether horizontal cursor movement through right-to-left (Arabic, Hebrew) text is visual (pressing the left arrow moves the cursor left) or logical (pressing the left arrow moves to the next lower index in the string, which is visually right in right-to-left text). The default is false on Windows, and true on other platforms.
keyMap (string): Configures the keymap to use. The default is "default", which is the only keymap defined in codemirror.js itself. Extra keymaps are found in the keymap directory. See the section on keymaps for more information.
extraKeys (object): Can be used to specify extra keybindings for the editor, alongside the ones defined by keyMap. Should be either null, or a valid keymap value.
lineWrapping (boolean): Whether CodeMirror should scroll or wrap for long lines. Defaults to false (scroll).
lineNumbers (boolean): Whether to show line numbers to the left of the editor.
firstLineNumber (integer): At which number to start counting lines. Default is 1.
lineNumberFormatter (function): A function used to format line numbers. The function is passed the line number, and should return a string that will be shown in the gutter.
gutters (array): Can be used to add extra gutters (beyond or instead of the line number gutter). Should be an array of CSS class names, each of which defines a width (and optionally a background), and which will be used to draw the background of the gutters. May include the CodeMirror-linenumbers class, in order to explicitly set the position of the line number gutter (it will default to be to the right of all other gutters). These class names are the keys passed to setGutterMarker.
fixedGutter (boolean): Determines whether the gutter scrolls along with the content horizontally (false) or whether it stays fixed during horizontal scrolling (true, the default).
readOnly (boolean): This disables editing of the editor content by the user. If the special value "nocursor" is given (instead of simply true), focusing of the editor is also disallowed.
showCursorWhenSelecting (boolean): Whether the cursor should be drawn when a selection is active. Defaults to false.
undoDepth (integer): The maximum number of undo levels that the editor stores. Defaults to 40.
tabindex (integer): The tab index to assign to the editor. If not given, no tab index will be assigned.
autofocus (boolean): Can be used to make CodeMirror focus itself on initialization. Defaults to off. When fromTextArea is used, and no explicit value is given for this option, it will be set to true when either the source textarea is focused, or it has an autofocus attribute and no other element is focused.

Below this a few more specialized, low-level options are listed. These are only useful in very specific situations, you might want to skip them the first time you read this manual.

dragDrop (boolean): Controls whether drag-and-drop is enabled. On by default.
onDragEvent (function): When given, this will be called when the editor is handling a dragenter, dragover, or drop event. It will be passed the editor instance and the event object as arguments. The callback can choose to handle the event itself, in which case it should return true to indicate that CodeMirror should not do anything further.
onKeyEvent (function): This provides a rather low-level hook into CodeMirror's key handling. If provided, this function will be called on every keydown, keyup, and keypress event that CodeMirror captures. It will be passed two arguments, the editor instance and the key event. This key event is pretty much the raw key event, except that a stop() method is always added to it. You could feed it to, for example, jQuery.Event to further normalize it.
This function can inspect the key event, and handle it if it wants to. It may return true to tell CodeMirror to ignore the event. Be wary that, on some browsers, stopping a keydown does not stop the keypress from firing, whereas on others it does. If you respond to an event, you should probably inspect its type property and only do something when it is keydown (or keypress for actions that need character data).
cursorBlinkRate (number): Half-period in milliseconds used for cursor blinking. The default blink rate is 530ms.
cursorHeight (number): Determines the height of the cursor. Default is 1, meaning it spans the whole height of the line. For some fonts (and by some tastes) a smaller height (for example 0.85), which causes the cursor to not reach all the way to the bottom of the line, looks better
workTime, workDelay (number): Highlighting is done by a pseudo background-thread that will work for workTime milliseconds, and then use timeout to sleep for workDelay milliseconds. The defaults are 200 and 300, you can change these options to make the highlighting more or less aggressive.
pollInterval (number): Indicates how quickly CodeMirror should poll its input textarea for changes (when focused). Most input is captured by events, but some things, like IME input on some browsers, don't generate events that allow CodeMirror to properly detect it. Thus, it polls. Default is 100 milliseconds.
flattenSpans (boolean): By default, CodeMirror will combine adjacent tokens into a single span if they have the same class. This will result in a simpler DOM tree, and thus perform better. With some kinds of styling (such as rounded corners), this will change the way the document looks. You can set this option to false to disable this behavior.
viewportMargin (integer): Specifies the amount of lines that are rendered above and below the part of the document that's currently scrolled into view. This affects the amount of updates needed when scrolling, and the amount of work that such an update does. You should usually leave it at its default, 100. Can be set to Infinity to make sure the whole document is always rendered, and thus the browser's text search works on it. This will have bad effects on performance of big documents.

Events

A CodeMirror instance emits a number of events, which allow client code to react to various situations. These are registered with the on method (and removed with the off method). These are the events that fire on the instance object. The name of the event is followed by the arguments that will be passed to the handler. The instance argument always refers to the editor instance.

"change" (instance, changeObj): Fires every time the content of the editor is changed. The changeObj is a {from, to, text, next} object containing information about the changes that occurred as second argument. from and to are the positions (in the pre-change coordinate system) where the change started and ended (for example, it might be {ch:0, line:18} if the position is at the beginning of line #19). text is an array of strings representing the text that replaced the changed range (split by line). If multiple changes happened during a single operation, the object will have a next property pointing to another change object (which may point to another, etc).
"cursorActivity" (instance): Will be fired when the cursor or selection moves, or any change is made to the editor content.
"viewportChange" (instance, from, to): Fires whenever the view port of the editor changes (due to scrolling, editing, or any other factor). The from and to arguments give the new start and end of the viewport.
"gutterClick" (instance, line, gutter, clickEvent): Fires when the editor gutter (the line-number area) is clicked. Will pass the editor instance as first argument, the (zero-based) number of the line that was clicked as second argument, the CSS class of the gutter that was clicked as third argument, and the raw mousedown event object as fourth argument.
"focus", "blur" (instance): These fire whenever the editor is focused or unfocused.
"scroll" (instance): Fires when the editor is scrolled.
"update" (instance): Will be fired whenever CodeMirror updates its DOM display.

It is also possible to register events on other objects. Line handles (as returned by, for example, getLineHandle) can be listened on with CodeMirror.on(handle, "delete", myFunc). They support the following events:

"delete" (): Will be fired when the line object is deleted. A line object is associated with the start of the line. Mostly useful when you need to find out when your gutter markers on a given line are removed.
"change" (): Fires when the line's text content is changed in any way (but the line is not deleted outright).

Marked range handles, as returned by markText, emit the following event:

"clear" (): Fired when the range is cleared, either through cursor movement in combination with clearOnEnter or through a call to its clear() method. Will only be fired once per handle. Note that deleting the range through text editing does not fire this event, because an undo action might bring the range back into existence.

Keymaps

Keymaps are ways to associate keys with functionality. A keymap is an object mapping strings that identify the keys to functions that implement their functionality.

Keys are identified either by name or by character. The CodeMirror.keyNames object defines names for common keys and associates them with their key codes. Examples of names defined here are Enter, F5, and Q. These can be prefixed with Shift-, Cmd-, Ctrl-, and Alt- (in that order!) to specify a modifier. So for example, Shift-Ctrl-Space would be a valid key identifier.

Alternatively, a character can be specified directly by surrounding it in single quotes, for example '$' or 'q'. Due to limitations in the way browsers fire key events, these may not be prefixed with modifiers.

The CodeMirror.keyMap object associates keymaps with names. User code and keymap definitions can assign extra properties to this object. Anywhere where a keymap is expected, a string can be given, which will be looked up in this object. It also contains the "default" keymap holding the default bindings.

The values of properties in keymaps can be either functions of a single argument (the CodeMirror instance), strings, or false. Such strings refer to properties of the CodeMirror.commands object, which defines a number of common commands that are used by the default keybindings, and maps them to functions. If the property is set to false, CodeMirror leaves handling of the key up to the browser. A key handler function may throw CodeMirror.Pass to indicate that it has decided not to handle the key, and other handlers (or the default behavior) should be given a turn.

Keys mapped to command names that start with the characters "go" (which should be used for cursor-movement actions) will be fired even when an extra Shift modifier is present (i.e. "Up": "goLineUp" matches both up and shift-up). This is used to easily implement shift-selection.

Keymaps can defer to each other by defining a fallthrough property. This indicates that when a key is not found in the map itself, one or more other maps should be searched. It can hold either a single keymap or an array of keymaps.

When a keymap contains a nofallthrough property set to true, keys matched against that map will be ignored if they don't match any of the bindings in the map (no further child maps will be tried, and the default effect of inserting a character will not occur).

Customized Styling

Up to a certain extent, CodeMirror's look can be changed by modifying style sheet files. The style sheets supplied by modes simply provide the colors for that mode, and can be adapted in a very straightforward way. To style the editor itself, it is possible to alter or override the styles defined in codemirror.css.

Some care must be taken there, since a lot of the rules in this file are necessary to have CodeMirror function properly. Adjusting colors should be safe, of course, and with some care a lot of other things can be changed as well. The CSS classes defined in this file serve the following roles:

CodeMirror: The outer element of the editor. This should be used for the editor width, height, borders and positioning. Can also be used to set styles that should hold for everything inside the editor (such as font and font size), or to set a background.
CodeMirror-scroll: Whether the editor scrolls (overflow: auto + fixed height). By default, it does. Setting the CodeMirror class to have height: auto and giving this class overflow-x: auto; overflow-y: hidden; will cause the editor to resize to fit its content.
CodeMirror-focused: Whenever the editor is focused, the top element gets this class. This is used to hide the cursor and give the selection a different color when the editor is not focused.
CodeMirror-gutters: This is the backdrop for all gutters. Use it to set the default gutter background color, and optionally add a border on the right of the gutters.
CodeMirror-linenumbers: Use this for giving a background or width to the line number gutter.
CodeMirror-linenumber: Used to style the actual individual line numbers. These won't be children of the CodeMirror-linenumbers (plural) element, but rather will be absolutely positioned to overlay it. Use this to set alignment and text properties for the line numbers.
CodeMirror-lines: The visible lines. This is where you specify vertical padding for the editor content.
CodeMirror-cursor: The cursor is a block element that is absolutely positioned. You can make it look whichever way you want.
CodeMirror-selected: The selection is represented by span elements with this class.
CodeMirror-matchingbracket, CodeMirror-nonmatchingbracket: These are used to style matched (or unmatched) brackets.

If your page's style sheets do funky things to all div or pre elements (you probably shouldn't do that), you'll have to define rules to cancel these effects out again for elements under the CodeMirror class.

Themes are also simply CSS files, which define colors for various syntactic elements. See the files in the theme directory.

Programming API

A lot of CodeMirror features are only available through its API. Thus, you need to write code (or use add-ons) if you want to expose them to your users.

Whenever points in the document are represented, the API uses objects with line and ch properties. Both are zero-based. CodeMirror makes sure to 'clip' any positions passed by client code so that they fit inside the document, so you shouldn't worry too much about sanitizing your coordinates. If you give ch a value of null, or don't specify it, it will be replaced with the length of the specified line.

getValue() → string

Get the current editor content. You can pass it an optional argument to specify the string to be used to separate lines (defaults to "\n").

setValue(string)

Set the editor content.

lineCount() → number

Get the number of lines in the editor.

getRange(from, to) → string

Get the text between the given points in the editor, which should be {line, ch} objects. An optional third argument can be given to indicate the line separator string to use (defaults to "\n").

replaceRange(string, from, to)

Replace the part of the document between from and to with the given string. from and to must be {line, ch} objects. to can be left off to simply insert the string at position from.

getSelection() → string

Get the currently selected code.

replaceSelection(string)

Replace the selection with the given string.

getCursor(start) → object

start is a boolean indicating whether the start or the end of the selection must be retrieved. If it is not given, the current cursor pos, i.e. the side of the selection that would move if you pressed an arrow key, is chosen. Alternatively, you can pass one of the strings "start", "end", "head" (same as not passing anything), or "anchor" (the opposite). A {line, ch} object will be returned.

somethingSelected() → boolean

Return true if any text is selected.

setCursor(pos)

Set the cursor position. You can either pass a single {line, ch} object, or the line and the character as two separate parameters.

setSelection(anchor, head)

Set the selection range. anchor and head should be {line, ch} objects. head defaults to anchor when not given.

getLine(n) → string

Get the content of line n.

setLine(n, text)

Set the content of line n.

removeLine(n)

Remove the given line from the document.

setSize(width, height)

Programatically set the size of the editor (overriding the applicable CSS rules). width and height height can be either numbers (interpreted as pixels) or CSS units ("100%", for example). You can pass null for either of them to indicate that that dimension should not be changed.

focus()

Give the editor focus.

scrollTo(x, y)

Scroll the editor to a given (pixel) position. Both arguments may be left as null or undefined to have no effect.

getScrollInfo()

Get an

{left, top, width, height, clientWidth,
      clientHeight}

object that represents the current scroll position, the size of the scrollable area, and the size of the visible area (minus scrollbars).

scrollIntoView(pos)

Scrolls the given element into view. pos may be either a {line, ch} position, referring to a given character, null, to refer to the cursor, or a {left, top, right, bottom} object, in editor-local coordinates.

setOption(option, value)

Change the configuration of the editor. option should the name of an option, and value should be a valid value for that option.

getOption(option) → value

Retrieves the current value of the given option for this editor instance.

getMode() → object

Gets the mode object for the editor. Note that this is distinct from getOption("mode"), which gives you the mode specification, rather than the resolved, instantiated mode object.

addKeyMap(map)

Attach an additional keymap to the editor. This is mostly useful for add-ons that need to register some key handlers without trampling on the extraKeys option. Maps added in this way have a lower precedence than extraKeys, a higher precedence than the base keyMap, and between them, the maps added earlier have a higher precedence than those added later.

removeKeyMap(map)

Disable a keymap added with addKeyMap. Either pass in the keymap object itself, or a string, which will be compared against the name property of the active keymaps.

addOverlay(mode, options)

Enable a highlighting overlay. This is a stateless mini-mode that can be used to add extra highlighting. For example, the search add-on uses it to highlight the term that's currently being searched. mode can be a mode spec or a mode object (an object with a token method). The option parameter is optional. If given it should be an object. Currently, only the opaque option is recognized. This defaults to off, but can be given to allow the overlay styling, when not null, to override the styling of the base mode entirely, instead of the two being applied together.

removeOverlay(mode)

Pass this the exact argument passed for the mode parameter to addOverlay to remove an overlay again.

on(type, func)

Register an event handler for the given event type (a string) on the editor instance. There is also a CodeMirror.on(object, type, func) version that allows registering of events on any object.

off(type, func)

Remove an event handler on the editor instance. An equivalent

CodeMirror.off(object, type,
      func)

also exists.

cursorCoords(where, mode) → object

Returns an {left, top, bottom} object containing the coordinates of the cursor position. If mode is "local", they will be relative to the top-left corner of the editable document. If it is "page" or not given, they are relative to the top-left corner of the page. where can be a boolean indicating whether you want the start (true) or the end (false) of the selection, or, if a

{line,
      ch}

object is given, it specifies the precise position at which you want to measure.

charCoords(pos, mode) → object

Returns the position and dimensions of an arbitrary character. pos should be a {line, ch} object. This differs from cursorCoords in that it'll give the size of the whole character, rather than just the position that the cursor would have when it would sit at that position.

coordsChar(object) → pos

Given an {left, top} object (in page coordinates), returns the {line, ch} position that corresponds to it.

defaultTextHeight() → number

Returns the line height of the default font for the editor.

markClean()

Set the editor content as 'clean', a flag that it will retain until it is edited, and which will be set again when such an edit is undone again. Useful to track whether the content needs to be saved.

isClean() → boolean

Returns whether the document is currently clean (not modified since initialization or the last call to markClean).

undo()

Undo one edit (if any undo events are stored).

redo()

Redo one undone edit.

historySize() → object

Returns an object with {undo, redo} properties, both of which hold integers, indicating the amount of stored undo and redo operations.

clearHistory()

Clears the editor's undo history.

getHistory() → object

Get a (JSON-serializeable) representation of the undo history.

setHistory(object)

Replace the editor's undo history with the one provided, which must be a value as returned by getHistory. Note that this will have entirely undefined results if the editor content isn't also the same as it was when getHistory was called.

indentLine(line, dir)

Adjust the indentation of the given line. The second argument (which defaults to "smart") may be one of:

"prev": Base indentation on the indentation of the previous line.
"smart": Use the mode's smart indentation if available, behave like "prev" otherwise.
"add": Increase the indentation of the line by one indent unit.
"subtract": Reduce the indentation of the line.

getTokenAt(pos) → object

Retrieves information about the token the current mode found before the given position (a {line, ch} object). The returned object has the following properties:

start: The character (on the given line) at which the token starts.
end: The character at which the token ends.
string: The token's string.
type: The token type the mode assigned to the token, such as "keyword" or "comment" (may also be null).
state: The mode's state at the end of this token.

markText(from, to, options) → object

Can be used to mark a range of text with a specific CSS class name. from and to should be {line, ch} objects. The options parameter is optional. When given, it should be an object that may contain the following configuration options:

className (string): Assigns a CSS class to the marked stretch of text.
inclusiveLeft (boolean): Determines whether text inserted on the left of the marker will end up inside or outside of it.
inclusiveRight (boolean): Like inclusiveLeft, but for the right side.
atomic (boolean): Atomic ranges act as a single unit when cursor movement is concerned—i.e. it is impossible to place the cursor inside of them. In atomic ranges, inclusiveLeft and inclusiveRight have a different meaning—they will prevent the cursor from being placed respectively directly before and directly after the range.
collapsed (boolean): Collapsed ranges do not show up in the display. Setting a range to be collapsed will automatically make it atomic.
clearOnEnter (boolean): When enabled, will cause the mark to clear itself whenever the cursor enters its range. This is mostly useful for text-replacement widgets that need to 'snap open' when the user tries to edit them. A the "clear" event fired on the range handle can be used to be notified when this happens.
replacedWith (dom node): Use a given node to display this range. Implies both collapsed and atomic. The given DOM node must be an inline element (as opposed to a block element).
readOnly: A read-only span can, as long as it is not cleared, not be modified except by calling setValue to reset the whole document. Note: adding a read-only span currently clears the undo history of the editor, because existing undo events being partially nullified by read-only spans would corrupt the history (in the current implementation).
startStyle: Can be used to specify an extra CSS class to be applied to the leftmost span that is part of the marker.
endStyle: Equivalent to startStyle, but for the rightmost span.

The method will return an object that represents the marker (with constuctor CodeMirror.TextMarker), which exposes three methods: clear(), to remove the mark, find(), which returns a {from, to} object (both holding document positions), indicating the current position of the marked range, or undefined if the marker is no longer in the document, and finally getOptions(copyWidget), which returns an object representing the options for the marker. If copyWidget is given an true, it will clone the value of the replacedWith option, if any.

setBookmark(pos, widget) → object

Inserts a bookmark, a handle that follows the text around it as it is being edited, at the given position. A bookmark has two methods find() and clear(). The first returns the current position of the bookmark, if it is still in the document, and the second explicitly removes the bookmark. The widget argument is optional, and can be used to display a DOM node at the current location of the bookmark (analogous to the replacedWith option to markText).

findMarksAt(pos) → array

Returns an array of all the bookmarks and marked ranges present at the given position.

setGutterMarker(line, gutterID, value) → lineHandle

Sets the gutter marker for the given gutter (identified by its CSS class, see the gutters option) to the given value. Value can be either null, to clear the marker, or a DOM element, to set it. The DOM element will be shown in the specified gutter next to the specified line.

clearGutter(gutterID)

Remove all gutter markers in the gutter with the given ID.

addLineClass(line, where, class) → lineHandle

Set a CSS class name for the given line. line can be a number or a line handle. where determines to which element this class should be applied, can can be one of "text" (the text element, which lies in front of the selection), "background" (a background element that will be behind the selection), or "wrap" (the wrapper node that wraps all of the line's elements, including gutter elements). class should be the name of the class to apply.

removeLineClass(line, where, class) → lineHandle

Remove a CSS class from a line. line can be a line handle or number. where should be one of "text", "background", or "wrap" (see addLineClass). class can be left off to remove all classes for the specified node, or be a string to remove only a specific class.

lineInfo(line) → object

Returns the line number, text content, and marker status of the given line, which can be either a number or a line handle. The returned object has the structure

{line, handle, text,
      gutterMarkers, textClass, bgClass, wrapClass, widgets}

, where gutterMarkers is an object mapping gutter IDs to marker elements, and widgets is an array of line widgets attached to this line, and the various class properties refer to classes added with addLineClass.

getLineHandle(num) → lineHandle

Fetches the line handle for the given line number.

getLineNumber(handle) → integer

Given a line handle, returns the current position of that line (or null when it is no longer in the document).

getViewport() → object

Returns a {from, to} object indicating the start (inclusive) and end (exclusive) of the currently displayed part of the document. In big documents, when most content is scrolled out of view, CodeMirror will only render the visible part, and a margin around it. See also the viewportChange event.

addWidget(pos, node, scrollIntoView)

Puts node, which should be an absolutely positioned DOM node, into the editor, positioned right below the given {line, ch} position. When scrollIntoView is true, the editor will ensure that the entire node is visible (if possible). To remove the widget again, simply use DOM methods (move it somewhere else, or call removeChild on its parent).

addLineWidget(line, node, options) → object

Adds a line widget, an element shown below a line, spanning the whole of the editor's width, and moving the lines below it downwards. line should be either an integer or a line handle, and node should be a DOM node, which will be displayed below the given line. options, when given, should be an object that configures the behavior of the widget. The following options are supported (all default to false):

coverGutter (boolean): Whether the widget should cover the gutter.
noHScroll (boolean): Whether the widget should stay fixed in the face of horizontal scrolling.
above (boolean): Causes the widget to be placed above instead of below the text of the line.
showIfHidden (boolean): When true, will cause the widget to be rendered even if the line it is associated with is hidden.

Note that the widget node will become a descendant of nodes with CodeMirror-specific CSS classes, and those classes might in some cases affect it. This method returns an object that represents the widget placement. It'll have a line property pointing at the line handle that it is associated with, and the following methods:

clear(): Removes the widget.
changed(): Call this if you made some change to the widget's DOM node that might affect its height. It'll force CodeMirror to update the height of the line that contains the widget.

posFromIndex(index) → object

Calculates and returns a {line, ch} object for a zero-based index who's value is relative to the start of the editor's text. If the index is out of range of the text then the returned object is clipped to start or end of the text respectively.

indexFromPos(object) → number

The reverse of posFromIndex.

The following are more low-level methods:

operation(func) → result: CodeMirror internally buffers changes and only updates its DOM structure after it has finished performing some operation. If you need to perform a lot of operations on a CodeMirror instance, you can call this method with a function argument. It will call the function, buffering up all changes, and only doing the expensive update after the function returns. This can be a lot faster. The return value from this method will be the return value of your function.
refresh(): If your code does something to change the size of the editor element (window resizes are already listened for), or unhides it, you should probably follow up by calling this method to ensure CodeMirror is still looking as intended.
extendSelection(pos, pos2): Similar to setSelection, but will, if shift is held or the extending flag is set, move the head of the selection while leaving the anchor at its current place. pos2 is optional, and can be passed to ensure a region (for example a word or paragraph) will end up selected (in addition to whatever lies between that region and the current anchor).
setExtending(bool): Sets or clears the 'extending' flag, which acts similar to the shift key, in that it will cause cursor movement and calls to extendSelection to leave the selection anchor in place.
getInputField() → textarea: Returns the hidden textarea used to read input.
getWrapperElement() → node: Returns the DOM node that represents the editor, and controls its size. Remove this from your tree to delete an editor instance.
getScrollerElement() → node: Returns the DOM node that is responsible for the scrolling of the editor.
getGutterElement() → node: Fetches the DOM node that contains the editor gutters.
getStateAfter(line) → state: Returns the mode's parser state, if any, at the end of the given line number. If no line number is given, the state at the end of the document is returned. This can be useful for storing parsing errors in the state, or getting other kinds of contextual information for a line.

The CodeMirror object itself provides several useful properties. Firstly, its version property contains a string that indicates the version of the library. For releases, this simply contains "major.minor" (for example "2.33". For beta versions, " B" (space, capital B) is added at the end of the string, for development snapshots, " +" (space, plus) is added.

The CodeMirror.fromTextArea method provides another way to initialize an editor. It takes a textarea DOM node as first argument and an optional configuration object as second. It will replace the textarea with a CodeMirror instance, and wire up the form of that textarea (if any) to make sure the editor contents are put into the textarea when the form is submitted. A CodeMirror instance created this way has three additional methods:

save(): Copy the content of the editor into the textarea.
toTextArea(): Remove the editor, and restore the original textarea (with the editor's current content).
getTextArea() → textarea: Returns the textarea that the instance was based on.

If you want to define extra methods in terms of the CodeMirror API, it is possible to use CodeMirror.defineExtension(name, value). This will cause the given value (usually a method) to be added to all CodeMirror instances created from then on.

Similarly, CodeMirror.defineOption(name, default, updateFunc) can be used to define new options for CodeMirror. The updateFunc will be called with the editor instance and the new value when an editor is initialized, and whenever the option is modified through setOption.

If your extention just needs to run some code whenever a CodeMirror instance is initialized, use CodeMirror.defineInitHook. Give it a function as its only argument, and from then on, that function will be called (with the instance as argument) whenever a new CodeMirror instance is initialized.

Add-ons

The addon directory in the distribution contains a number of reusable components that implement extra editor functionality. In brief, they are:

dialog.js

Provides a very simple way to query users for text input. Adds an openDialog method to CodeMirror instances, which can be called with an HTML fragment that provides the prompt (should include an input tag), and a callback function that is called when text has been entered. Depends on addon/dialog/dialog.css.

searchcursor.js

Adds the

getSearchCursor(query, start, caseFold) →
      cursor

method to CodeMirror instances, which can be used to implement search/replace functionality. query can be a regular expression or a string (only strings will match across lines—if they contain newlines). start provides the starting position of the search. It can be a {line, ch} object, or can be left off to default to the start of the document. caseFold is only relevant when matching a string. It will cause the search to be case-insensitive. A search cursor has the following methods:

findNext(), findPrevious() → boolean: Search forward or backward from the current position. The return value indicates whether a match was found. If matching a regular expression, the return value will be the array returned by the match method, in case you want to extract matched groups.
from(), to() → object: These are only valid when the last call to findNext or findPrevious did not return false. They will return {line, ch} objects pointing at the start and end of the match.
replace(text): Replaces the currently found match with the given text and adjusts the cursor position to reflect the replacement.

search.js

Implements the search commands. CodeMirror has keys bound to these by default, but will not do anything with them unless an implementation is provided. Depends on searchcursor.js, and will make use of openDialog when available to make prompting for search queries less ugly.

matchbrackets.js

Defines an option matchBrackets which, when set to true, causes matching brackets to be highlighted whenever the cursor is next to them. It also adds a method matchBrackets that forces this to happen once, and a method findMatchingBracket that can be used to run the bracket-finding algorithm that this uses internally.

foldcode.js

Helps with code folding. See the demo for an example. Call CodeMirror.newFoldFunction with a range-finder helper function to create a function that will, when applied to a CodeMirror instance and a line number, attempt to fold or unfold the block starting at the given line. A range-finder is a language-specific function that also takes an instance and a line number, and returns an range to be folded, or null if no block is started on that line. This file provides CodeMirror.braceRangeFinder, which finds blocks in brace languages (JavaScript, C, Java, etc), CodeMirror.indentRangeFinder, for languages where indentation determines block structure (Python, Haskell), and CodeMirror.tagRangeFinder, for XML-style languages.

collapserange.js

Another approach to folding. See demo. Allows the user to select a range to fold by clicking in the gutter.

runmode.js

Can be used to run a CodeMirror mode over text without actually opening an editor instance. See the demo for an example. There alternate version of the file avaible for running stand-alone (without including all of CodeMirror) and for running under node.js.

overlay.js

Mode combinator that can be used to extend a mode with an 'overlay' — a secondary mode is run over the stream, along with the base mode, and can color specific pieces of text without interfering with the base mode. Defines CodeMirror.overlayMode, which is used to create such a mode. See this demo for a detailed example.

multiplex.js

Mode combinator that can be used to easily 'multiplex' between several modes. Defines CodeMirror.multiplexingMode which, when given as first argument a mode object, and as other arguments any number of {open, close, mode [, delimStyle]} objects, will return a mode object that starts parsing using the mode passed as first argument, but will switch to another mode as soon as it encounters a string that occurs in one of the open fields of the passed objects. When in a sub-mode, it will go back to the top mode again when the close string is encountered. Pass "\n" for open or close if you want to switch on a blank line. When delimStyle is specified, it will be the token style returned for the delimiter tokens. The outer mode will not see the content between the delimiters. See this demo for an example.

simple-hint.js

Provides a framework for showing autocompletion hints. Defines CodeMirror.simpleHint, which takes a CodeMirror instance and a hinting function, and pops up a widget that allows the user to select a completion. Hinting functions are function that take an editor instance, and return a {list, from, to} object, where list is an array of strings (the completions), and from and to give the start and end of the token that is being completed. Depends on addon/hint/simple-hint.css.

javascript-hint.js

Defines CodeMirror.javascriptHint and CodeMirror.coffeescriptHint, which are simple hinting functions for the JavaScript and CoffeeScript modes.

xml-hint.js

Defines CodeMirror.xmlHint, a hinting function for XML (which requires a schema to be defined).

python-hint.js

Defines CodeMirror.pythonHint, a hinter for Python code.

match-highlighter.js

Adds a matchHighlight method to CodeMirror instances that can be called (typically from a cursorActivity handler) to highlight all instances of a currently selected word with the a classname given as a first argument to the method. Depends on the searchcursor add-on. Demo here.

formatting.js

Adds commentRange, autoIndentRange, and autoFormatRange methods that, respectively, comment (or uncomment), indent, or format (add line breaks) a range of code. Demo here.

closetag.js

Provides utility functions for adding automatic tag closing to XML modes. See the demo.

loadmode.js

Defines a

CodeMirror.requireMode(modename,
      callback)

function that will try to load a given mode and call the callback when it succeeded. You'll have to set CodeMirror.modeURL to a string that mode paths can be constructed from, for example "mode/%N/%N.js"—the %N's will be replaced with the mode name. Also defines CodeMirror.autoLoadMode(instance, mode), which will ensure the given mode is loaded and cause the given editor instance to refresh its mode when the loading succeeded. See the demo.

continuecomment.js

Adds a command called newlineAndIndentContinueComment that you can bind Enter to in order to have the editor prefix new lines inside C-like block comments with an asterisk.

Writing CodeMirror Modes

Modes typically consist of a single JavaScript file. This file defines, in the simplest case, a lexer (tokenizer) for your language—a function that takes a character stream as input, advances it past a token, and returns a style for that token. More advanced modes can also handle indentation for the language.

The mode script should call CodeMirror.defineMode to register itself with CodeMirror. This function takes two arguments. The first should be the name of the mode, for which you should use a lowercase string, preferably one that is also the name of the files that define the mode (i.e. "xml" is defined in xml.js). The second argument should be a function that, given a CodeMirror configuration object (the thing passed to the CodeMirror function) and an optional mode configuration object (as in the mode option), returns a mode object.

Typically, you should use this second argument to defineMode as your module scope function (modes should not leak anything into the global scope!), i.e. write your whole mode inside this function.

The main responsibility of a mode script is parsing the content of the editor. Depending on the language and the amount of functionality desired, this can be done in really easy or extremely complicated ways. Some parsers can be stateless, meaning that they look at one element (token) of the code at a time, with no memory of what came before. Most, however, will need to remember something. This is done by using a state object, which is an object that is always passed when reading a token, and which can be mutated by the tokenizer.

Modes that use a state must define a startState method on their mode object. This is a function of no arguments that produces a state object to be used at the start of a document.

The most important part of a mode object is its token(stream, state) method. All modes must define this method. It should read one token from the stream it is given as an argument, optionally update its state, and return a style string, or null for tokens that do not have to be styled. For your styles, you are encouraged to use the 'standard' names defined in the themes (without the cm- prefix). If that fails, it is also possible to come up with your own and write your own CSS theme file.

The stream object that's passed to token encapsulates a line of code (tokens may never span lines) and our current position in that line. It has the following API:

eol() → boolean: Returns true only if the stream is at the end of the line.
sol() → boolean: Returns true only if the stream is at the start of the line.
peek() → character: Returns the next character in the stream without advancing it. Will return an null at the end of the line.
next() → character: Returns the next character in the stream and advances it. Also returns null when no more characters are available.
eat(match) → character: match can be a character, a regular expression, or a function that takes a character and returns a boolean. If the next character in the stream 'matches' the given argument, it is consumed and returned. Otherwise, undefined is returned.
eatWhile(match) → boolean: Repeatedly calls eat with the given argument, until it fails. Returns true if any characters were eaten.
eatSpace() → boolean: Shortcut for eatWhile when matching white-space.
skipToEnd(): Moves the position to the end of the line.
skipTo(ch) → boolean: Skips to the next occurrence of the given character, if found on the current line (doesn't advance the stream if the character does not occur on the line). Returns true if the character was found.
match(pattern, consume, caseFold) → boolean: Act like a multi-character eat—if consume is true or not given—or a look-ahead that doesn't update the stream position—if it is false. pattern can be either a string or a regular expression starting with ^. When it is a string, caseFold can be set to true to make the match case-insensitive. When successfully matching a regular expression, the returned value will be the array returned by match, in case you need to extract matched groups.
backUp(n): Backs up the stream n characters. Backing it up further than the start of the current token will cause things to break, so be careful.
column() → integer: Returns the column (taking into account tabs) at which the current token starts.
indentation() → integer: Tells you how far the current line has been indented, in spaces. Corrects for tab characters.
current() → string: Get the string between the start of the current token and the current stream position.

By default, blank lines are simply skipped when tokenizing a document. For languages that have significant blank lines, you can define a blankLine(state) method on your mode that will get called whenever a blank line is passed over, so that it can update the parser state.

Because state object are mutated, and CodeMirror needs to keep valid versions of a state around so that it can restart a parse at any line, copies must be made of state objects. The default algorithm used is that a new state object is created, which gets all the properties of the old object. Any properties which hold arrays get a copy of these arrays (since arrays tend to be used as mutable stacks). When this is not correct, for example because a mode mutates non-array properties of its state object, a mode object should define a copyState method, which is given a state and should return a safe copy of that state.

If you want your mode to provide smart indentation (through the indentLine method and the indentAuto and newlineAndIndent commands, which keys can be bound to), you must define an indent(state, textAfter) method on your mode object.

The indentation method should inspect the given state object, and optionally the textAfter string, which contains the text on the line that is being indented, and return an integer, the amount of spaces to indent. It should usually take the indentUnit option into account.

Finally, a mode may define an electricChars property, which should hold a string containing all the characters that should trigger the behaviour described for the electricChars option.

So, to summarize, a mode must provide a token method, and it may provide startState, copyState, and indent methods. For an example of a trivial mode, see the diff mode, for a more involved example, see the C-like mode.

Sometimes, it is useful for modes to nest—to have one mode delegate work to another mode. An example of this kind of mode is the mixed-mode HTML mode. To implement such nesting, it is usually necessary to create mode objects and copy states yourself. To create a mode object, there are CodeMirror.getMode(options, parserConfig), where the first argument is a configuration object as passed to the mode constructor function, and the second argument is a mode specification as in the mode option. To copy a state object, call CodeMirror.copyState(mode, state), where mode is the mode that created the given state.

In a nested mode, it is recommended to add an extra methods, innerMode which, given a state object, returns a {state, mode} object with the inner mode and its state for the current position. These are used by utility scripts such as the autoformatter and the tag closer to get context information. Use the CodeMirror.innerMode helper function to, starting from a mode and a state, recursively walk down to the innermost mode and state.

To make indentation work properly in a nested parser, it is advisable to give the startState method of modes that are intended to be nested an optional argument that provides the base indentation for the block of code. The JavaScript and CSS parser do this, for example, to allow JavaScript and CSS code inside the mixed-mode HTML mode to be properly indented.

It is possible, and encouraged, to associate your mode, or a certain configuration of your mode, with a MIME type. For example, the JavaScript mode associates itself with text/javascript, and its JSON variant with application/json. To do this, call CodeMirror.defineMIME(mime, modeSpec), where modeSpec can be a string or object specifying a mode, as in the mode option.

Sometimes, it is useful to add or override mode object properties from external code. The CodeMirror.extendMode can be used to add properties to mode objects produced for a specific mode. Its first argument is the name of the mode, its second an object that specifies the properties that should be added. This is mostly useful to add utilities that can later be looked up through getMode.

Overview
Basic Usage
Configuration
Events
Keymaps
Customized Styling
Programming API
Add-ons
Writing CodeMirror Modes

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