CodeMirror is a code-editor component that can be embedded in Web pages. It 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.
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 few
modes (see the mode/
directory), and it isn't hard
to write new ones for other languages.
The easiest way to use CodeMirror is to simply load the script
and style sheet found under lib/
in the distribution,
plus the script and style sheet for the mode you want to use. For
example:
<script src="lib/codemirror.js"></script> <link rel="stylesheet" href="lib/codemirror.css"> <script src="mode/javascript/javascript.js"></script> <link rel="stylesheet" href="mode/javascript/javascript.css">
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(myTextArea, elt); }, {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 when the form (if it is part of a form) is submitted. See the API reference for a full description of this method.
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 options is bound to lead to odd errors.
These are the supported options:
value (string)
mode (string or object)
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.indentUnit (integer)
indentWithTabs (boolean)
tabMode (string)
"classic" (the default)
"shift"
mode."shift"
indentUnit
.
If shift was held while pressing tab, un-indent all selected
lines one unit."indent"
"default"
enterMode (string)
"indent" (the default)
"keep"
"flat"
lineNumbers
(boolean)firstLineNumber
(integer)gutter (boolean)
readOnly (boolean)
onChange (function)
onCursorActivity (function)
onChange
, but will also be called when the
cursor moves without any changes being made.onGutterClick (function)
matchBrackets (boolean)
workTime, workDelay (number)
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.undoDepth (integer)
tabindex (integer)
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
overflow: auto
+ fixed height). Can
also be used to set styles that should hold for everything
inside the editor, or to set a background.CodeMirror-focused
CodeMirror-gutter
CodeMirror-lines
class. Also, for the numbers
to line up, you'll want them to use exactly the same font as
normal edited text in CodeMirror-lines
. By default,
the gutter is 'fluid', meaning it will adjust its width to the
maximum line number or line marker width. You can also set a
fixed width if you want.CodeMirror-lines
CodeMirror-gutter
should have the same
padding.CodeMirror-cursor
CodeMirror-selected
span
elements
with this class.CodeMirror-matchingbracket
,
CodeMirror-matchingbracket
The actual lines, as well as the cursor, are represented
by pre
elements. By default no text styling (such as
bold) that might change line height is applied. If you do want
such effects, you'll have to give CodeMirror pre
a
fixed height. Also, you must still take care that character width
is constant.
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.
A lot of CodeMirror features are only available through its API. This has the disadvantage that you need to do work to enable them, and the advantage that CodeMirror will fit seamlessly into your application.
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.
getValue() → string
setValue(string)
getSelection() → string
replaceSelection(string)
focus()
setOption(option, value)
option
should the name of an option,
and value
should be a valid value for that
option.cursorCoords(start) → object
{x, y, yBot}
object containing the
coordinates of the cursor relative to the top-left corner of the
page. yBot
is the coordinate of the bottom of the
cursor. start
is a boolean indicating whether you
want the start or the end of the selection.undo()
redo()
getSearchCursor(query, start, caseFold) → cursor
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
match
method, in case you
want to extract matched groups.from(), to() → object
findNext
or findPrevious
did
not return false. They will return {line, ch}
objects pointing at the start and end of the match.markText(from, to, className) → function
from
and to
should
be {line, ch}
objects. The method will return a
function that can be called to remove the marking.setMarker(line, text, className) → lineHandle
text
and className
are
optional. Setting text
to a Unicode character like ◆
tends to give a nice effect. To put a picture in the gutter,
set text
to a space and className
to
something that sets a background image.clearMarker(line)
setMarker
. line
can be either a
number or a handle returned by setMarker
(since a
number may now refer to a different line if something was added
or deleted).matchBrackets()
lineCount() → number
getCursor(start) → object
start
is a boolean indicating whether the start
or the end of the selection must be retrieved. A {line,
ch}
object will be returned.setCursor(pos)
{line, ch}
object, or the line and the
character as two separate parameters.setSelection(start, end)
start
and end
should be {line, ch}
objects.getLine(n) → string
n
.setLine(n, text)
n
.removeLine(n)
replaceRange(string, from, to)
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
.The following are more low-level methods:
operation(func) → result
refresh()
getInputField() → textarea
Finally, the CodeMirror
object
itself has a method fromTextArea
. This 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 two
additional methods:
save()
toTextArea()
Modes typically consist of a JavaScript file and a CSS file.
The CSS file (see, for
example javascript.css
)
defines the classes that will be used to style the syntactic
elements of the code, and the script contains the logic to
actually assign these classes to the right pieces of text.
You'll usually want to use some kind of prefix for your CSS classes, so that they are unlikely to clash with other classes, both those used by other modes and those defined by the page in which CodeMirror is embedded.
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 xml.js
). The
second argument should a function that, given a CodeMirror
configuration object (the thing passed to
the CodeMirror
function) and a 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 can be mutated every time a new token is read.
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
CSS class string, or null
for tokens that do not have
to be styled.
The stream object encapsulates a line of code (tokens may never span lines) and our current position in that line. It has the following API:
eol() → boolean
peek() → character
undefined
at the end of the
line.next() → character
undefined
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) → integer
eat
with the given argument,
until it fails. Returns the amount of eaten characters.eatSpace() → integer
eatWhile
when matching
white-space.match(pattern, consume, caseFold) → boolean
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)
n
characters. Backing it up
further than the start of the current token will cause things to
break, so be careful.column() → integer
indentation() → integer
current() → string
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 have 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
(see entermode
and tabMode
when they
have a value of "indent"
), 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.
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 JavaScript
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.
Finally, it is possible 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.