0.1.2 • Public • Published


    This is a wrapper for Ace Editor to provide a 2-panel diffing/merging tool that visualizes differences in two documents and allows users to copy changes from to the other. If you're a developer, you've seen it a billion times; this is one for Ace Editor. :)

    It's built on top of the excellent, but appallingly-named google-diff-match-patch library (buuuurn). That lib handles the hard part: the computation of the document diffs. AceDiff just visualizes that information as line-diffs in the editors.

    NPM Dependencies

    This branch declares all its dependencies as NPM dependencies or peer-dependencies so that you should just be able to install the main module in your NPM project.

    • brace 0.8.0 or later (Ace Editor 1.2.3)
    • diff-match-patch


    Take a look at the gh-pages branch of this repo for some demos. The demos illustrate a few different configurations and styles. Hopefully they'll give you a rough sense of what it does and how it works.

    Fork: Demos 1 seems to work, 3 has wrong colors etc.


    • Compatible with any Ace Editor mode or theme
    • Accommodates realtime changes to one or both editors
    • Readonly option for left/right editors
    • full control over all CSS/IDs for styling. This includes styling the actual diffs and the SVG gutter lines.
    • control over how aggressively diffs are combined
    • option to allow users to copy diffs from one side to the other
    • option to either set the editor values by targeting markup containing the code, or by sending it via a config option
    • convenient API to do thing like changing options on the fly, getting the number of diffs, destroying it altogether.

    How to install

    Alrighty! Ace-diff requires you to do three things:

    • add some HTML to your page that includes three elements: the left editor, right editor, and a gutter element,
    • some JS to instantiate your AceDiff instance and set whatever settings you want,
    • some CSS to properly style the editors and gutter.

    Here's some token code so you can get a sense what's involved with these. But again, I'd really suggest checking out the demos for something more hands-on.


        <div id="left-editor"></div>
        <div id="gutter"></div>
        <div id="left-editor"></div>


    Here's an example of how you'd instantiate AceDiff. Note: it should be placed in a DOM ready function to ensure all code and DOM elements are available.

    var differ = new AceDiff({
      mode: "ace/mode/javascript",
      left: {
        id: "left-editor", //Instead of id, you can also pass the document element itself
        content: "your first file content here"
      right: {
        id: "right-editor",
        content: "your second file content here"


    Styling the elements is vitally important: the gutter should retain its width even if the user resizes his or her browser. But honestly, how you go about that is very much up to you: you can provide whatever CSS you want, depending on your scenario.

    If you want the ace editor's to change height/width based on a user's browser, I find using flexbox the best option - but hell, if you want to use a <table>, knock yourself out. :)

    Take a look at the demos for some ideas. They all use flexbox for the layouts, but include some different styles and class names just so you can see.


    You can configure your Ace-diff instance through a number of config settings. This object is what you pass to the constructor, like the Javascript section above.

    Default settings

    Here are all the defaults. I'll explain each one in details below. Note: you only need to override whatever you want.

      mode: null,
      theme: null,
      diffGranularity: 'broad',
      showDiffs: true,
      showConnectors: true,
      maxDiffs: 5000,
      left: {
        id: 'acediff-left-editor',
        content: null,
        mode: null,
        theme: null,
        editable: true,
        copyLinkEnabled: true
      right: {
        id: 'acediff-right-editor',
        content: null,
        mode: null,
        theme: null,
        editable: true,
        copyLinkEnabled: true
      classes: {
        gutterID: 'acediff-gutter',
        diff: 'acediff-diff',
        connector: 'acediff-connector',
        newCodeConnectorLink: 'acediff-new-code-connector-copy',
        newCodeConnectorLinkContent: '&#8594;',
        deletedCodeConnectorLink: 'acediff-deleted-code-connector-copy',
        deletedCodeConnectorLinkContent: '&#8592;',
        copyRightContainer: 'acediff-copy-right',
        copyLeftContainer: 'acediff-copy-left'

    Diffing settings

    • mode (string, required). this is the mode for the Ace Editor, e.g. "ace/mode/javascript". Check out the Ace docs for that. This setting will be applied to both editors. I figured 99.999999% of the time you're going to want the same mode for both of them so you can just set it once here. If you're a mad genius and want to have different modes for each side, (a) whoah man, what's your use-case?, and (b) you can override this setting in one of the settings below. Read on.
    • theme (string, optional). This lets you set the theme for both editors.
    • diffGranularity (string, optional, default: broad). this has two options (specific, and broad). Basically this determines how aggressively AceDiff combines diffs to simplify the interface. I found that often it's a judgement call as to whether multiple diffs on one side should be grouped. This setting provides a little control over it.
    • showDiffs (boolean, optional, default: true). Whether or not the diffs are enabled. This basically turns everything off.
    • showConnectors (boolean, optional, default: true). Whether or not the gutter in the middle show show connectors visualizing where the left and right changes map to one another.
    • maxDiffs (integer, optional, default: 5000). This was added a safety precaution. For really massive files with vast numbers of diffs, it's possible the Ace instances or AceDiff will become too laggy. This simply disables the diffing altogether once you hit a certain number of diffs.
    • left/right. this object contains settings specific to the leftmost editor.
    • / (string, optional, default: acediff-left-editor). The ID of the element where the leftmost editor will be created. That element can optionally contain the code you want to syntax highlight. If you don't care about the ID names, just leave this blank and give you element an ID of acediff-left-editor.
    • left.content / right.content (string, optional, default: null). If you like, when you instantiate AceDiff you can include the content that should appear in the leftmost editor via this property.
    • left.mode / right.mode (string, optional, defaults to whatever you entered in mode). This lets you override the default Ace Editor mode specified in mode.
    • left.theme / right.theme (string, optional, defaults to whatever you entered in theme). This lets you override the default Ace Editor theme specified in theme.
    • left.editable / right.editable (boolean, optional, default: true). Whether the left editor is editable or not.
    • left.copyLinkEnabled / right.copyLinkEnabled (boolean, optional, default: true). Whether the copy to right/left arrows should appear.


    • gutterID: the ID of the gutter element
    • gutterEl: instead of gutterID, the document element itself can be passed
    • diff: the class for a diff line on either editor
    • connector: the SVG connector
    • newCodeConnectorLink: the class for the copy-to-right links
    • newCodeConnectorLinkContent: the content of the copy to right link. Defaults to a unicode right arrow ('→')
    • deletedCodeConnectorLink: the class for the copy-to-left links
    • deletedCodeConnectorLinkContent: the content of the copy to left link. Defaults to a unicode right arrow ('←')
    • copyRightContainer: the class for a wrapper container containing in the copy-to-right links
    • copyLeftContainer: 'the class for a wrapper container containing in the copy-to-left links


    There are a few API methods available on your AceDiff instance.

    • aceInstance.getEditors(): this returns an object with left and right properties. Each contains a reference to the Ace editor, in case you need to do anything with them. Ace has a ton of options which I wasn't going to support via the wrapper. This should allow you to do whatever you need
    • aceInstance.setOptions(): this lets you set many of the above options on the fly. Note: certain things used during the construction of the editor, like the classes can't be overridden.
    • aceInstance.getNumDiffs(): returns the number of diffs currently being displayed.
    • aceInstance.diff(): updates the diff. This shouldn't ever be required because AceDiff automatically recognizes the key events like changes to the editor and window resizing. But I've included it because there may always be that fringe case...
    • aceInstance.destroy(): destroys the AceDiff instance. Basically this just destroys both editors and cleans out the gutter.

    Browser Support

    All modern non-IE browsers, and IE 10 and up. Open a ticket if you find otherwise.




    • 0.1.0 - March 21, 2015 - initial version


    npm i brace-diff

    DownloadsWeekly Downloads






    Last publish


    • fforw