# Upgrading from v2 to v3

MathJax v3 is a complete rewrite of MathJax from the ground up (see What’s New in MathJax v3.0), and so its internal structure is quite different from that of version 2. That means MathJax v3 is not a drop-in replacement for MathJax v2, and upgrading to version 3 takes some adjustment to your web pages. The sections below describe the changes you will need to make, and the most important differences between v2 and v3.

Warning

If you are using the `latest.js` feature of MathJax v2 on a CDN, note that this will not update to version 3 automatically, since there are significant and potentially breaking changes in version 3. There is, however, a bug in `latest.js` in versions 2.7.5 and below; when the current version is 3.0 or higher, `latest.js` will not use the highest version of 2.x, but instead will use the version from which `latest.js` has been taken. For example, if you load `latest.js` from version 2.7.3, it currently is giving you version 2.7.5 as the latest version, when version 3 is released to the CDN, your pages will revert to using version 2.7.3 again. This behavior has been corrected in version 2.7.6, so if you change to loading `latest.js` from version 2.7.6, you should get the latest 2.x version regardless of the presence of version 3 on the CDN.

MathJax v3 is still a work in progress; not all features of version 2 have been converted to version 3 yet, and some may not be. MathJax v2 will continue to be maintained as we work to move more features into version 3, but MathJax v2 likely will not see much further development, just maintenance, once MathJax v3 is fully converted.

- Configuration Changes

- Changes in Loading MathJax

- Changes in the MathJax API

- Changes in Input and Output Jax

- No Longer Applies to Version 3

- Not Yet Ported to Version 3

- Contextual Menu Changes

- MathJax in Node

- Version 2 Compatibility Example

## Configuration Changes

There are a number of changes in version 3 that affect how MathJax is configured. In version 2, there were several ways to provide configuration for MathJax; in MathJax 3, when you are using MathJax components, there is now only one, which is to set the `MathJax` global to contain the configuration information prior to loading MathJax. In particular, you no longer call `MathJax.Hub.Config()`, and this function does not exist in MathJax v3. See the section Configuring MathJax for more details on how to configure MathJax.

In addition to requiring the use of the `MathJax` global variable for setting the configuration, the organization of the configuration options have been changed to accommodate the new internal structure of MathJax, and some of their names have changed as well. To help you convert your existing version 2 configurations to version 3, we provide a conversion tool that you can use to obtain a version 3 configuration that is as close as possible to your current one.

Not all configuration parameters can be converted directly, however. For some of these, it is because the version 2 features have not yet been ported to version 3, but for others, the version 2 feature may simply not exist in the new architecture of version 3. For example, MathJax v2 updates the page in phases, first removing the math source expressions (e.g., the TeX code), then inserts a preview expression (fast to create, but not as accurately laid out), and then goes back and produces high-quality typeset versions, which it inserts in chunks between page updates. MathJax version 3 does not work that way (it does not change the page until the math is entirely typeset), and so the options that control the math preview and the chunking of the equations for display simply have no counterparts in version 3.

Finally, configurations that change the MathJax code via augmenting the existing MathJax objects, or that hook into MathJax’s processing pipeline via `MathJax.Hub.Register.StartupHook()` or one of the other hook mechanisms will not carry over to version 3. MathJax v3 does not use the queues, signals, and callbacks that are central to version 2, so code that relies on them will have to be updated. See the Configuring and Loading MathJax section for some approaches to these issues.

## Changes in Loading MathJax

Just as there are changes in how MathJax is configured, there are also changes in how MathJax is loaded. With version 2, you load `MathJax.js` and indicate a combined configuration file using `?config=` followed by the name of the configuration file. This always required at least two files to be loaded (and often more than that), and the second file was always loaded asynchronously, meaning MathJax always operated asynchronously.

In version 3, there is no longer a `MathJax.js` file, and you load a combined component file directly. E.g., you load `tex-chtml.js` to get TeX with CommonHTML output. This reduces the number of files that need to be requested, and improves performance. See Loading MathJax for more details.

Just as there is no need to use `?config=` in version 3, the other parameters that could be set in this way also are absent from version 3. So, for example, you can’t set `delayStartupUntil` in the script that loads MathJax.

The startup sequence operates fundamentally differently in version 3 from how it did in version 2. In version 2, MathJax would begin its startup process immediately upon MathJax being loaded, queuing action to perform configuration blocks, load extensions and jax, do the initial typesetting, and so on. It was difficult to insert your own actions into this sequence, and timing issues could occur if you didn’t put your configuration in the right place.

In version 3, synchronization with MathJax is done through ES6 promises, rather than MathJax’s queues and signals, and MathJax’s startup process is more straight-forward. You can insert your own code into the startup process more easily, and can replace the default startup actions entirely, if you wish. The actions MathJax takes during startup are better separated so that you can pick and choose the ones you want to perform. See the Startup Actions section for more details on how to accomplish this.

## Changes in the MathJax API

Because the internals have been completely redesigned, its API has changed, and so if you have been calling MathJax functions, or have modified MathJax internals by augmenting the existing MathJax objects, that code will no longer work with version 3, and will have to be modified. Some of the more important changes are discussed below.

- The `MathJax.Hub.Typeset()` function has been replaced by the `MathJax.typesetPromise()` and `MathJax.typeset()` functions. In fact, the `MathJax.Hub` has been removed entirely.

- The queues, signals, and callbacks that are central to version 2 have been replaced by ES6 promises in version 3. In particular, you can use `MathJax.startup.promise` as a replacement for `MathJax.Hub.Queue()`. See the Handling Asynchronous Typesetting section for how this is done. See the Version 2 Compatibility Example below for code that may make it possible for you to use your version 2 code in version 3.

- The `MathJax.Hub.Register.StartupHook()` and other related hooks have been replaced by `ready()` functions in the loader component. So code that relies on these hooks to alter MathJax need to be reworked. The Startup Actions section shows some mechanisms that can be used for this.

- Version 2 configurations could include an `Augment()` block that could be used to add (or override) methods and data in the main MathJax objects. In version 3, this should be handled through subclassing the MathJax object classes, and passing the new classes to the objects that use them. This can be done during the startup component’s `ready()` function, when the MathJax classes are available, but before any of their instances have been created. See the Startup Actions section for some ideas on how this can be done.

- The `Augment` configuration blocks and `StartupHooks()` function described above could be used in version 2 to extend MathJax’s capabilities, and in particular, to extend the TeX input jax by adding new javascript-based macros. These version-2 mechanisms are not available in version 3; instead, TeX extensions are more formalized in version 3. See the Building a Custom Component section for an example of how this can be done.

- In version 2, the mathematics that is located by MathJax is removed from the page and stored in special `<script>` tags within the page. These are not visible to the reader, but mark the location and content of the math on the page. It was possible in version 2 for programs to create these `<script>` tags themselves, avoiding the need for MathJax to look for math delimiters, and for the page author to encode HTML special characters like `<`, `>`, and `&` in their mathematics. Version 3 does not alter the document in this way, and does not store the math that it locates in tags in the page. Instead, it keeps an external list of math objects (of the `MathItem` class). So if you wish to use such scripts to store the math in the page initially, you can replace the `find` action in the renderActions list to use a function that locates the scripts and creates the needed `MathItem` objects. For example

      MathJax = {
        options: {
          renderActions: {
            find: [10, function (doc) {
              for (const node of document.querySelectorAll('script[type^="math/tex"]')) {
                const display = !!node.type.match(/; *mode=display/);
                const math = new doc.options.MathItem(node.textContent, doc.inputJax[0], display);
                const text = document.createTextNode('');
                node.parentNode.replaceChild(text, node);
                math.start = {node: text, delim: '', n: 0};
                math.end = {node: text, delim: '', n: 0};
                doc.math.push(math);
              }
            }, '']
          }
        }
      };

  should find the scripts that MathJax version 2 normally would have created.

  Note that this will replace the standard `find` action that looks for math delimiters with this one that looks for the MathJax v2 script tags instead. If you want to do both the original delimiter search and the search for script tags, then change the `find:` above to `findScript:` so that it doesn’t replace the default `find` action. That way, both actions will occur.

## Changes in Input and Output Jax

The input and output processors (called “jax”) are core pieces of MathJax. All three input processors from version 2 are present in version 3, but the AsciiMath processor has not been fully ported to version 3, and currently consists of the legacy version 2 code patched onto the version 3 framework. This is larger and less efficient than a full version 3 port, which should be included in a future release.

In version 2, MathJax used preprocessors (tex2jax, mml2jax, asciimath2jax, and jsMath2jax) to locate the mathematics in the page and prepare it for the input jax. There was really no need to have these be separate pieces, so in version 3, these have been folded into their respective input jax. That means that you don’t load them separately, and the configuration options of the preprocessor and input jax have been combined. For example, the `tex2jax` and `TeX` options now both occur in the `tex` configuration block.

MathJax version 2 included six different output jax, which had been developed over time to serve different purposes. The original HTML-CSS output jax had the greatest browser coverage, but its output was browser-dependent, its font detection was fragile, and it was the slowest of the output processors. The CommonHTML output jax was a more modern remake of the HTML output that was both browser independent, and considerably faster. The SVG output jax produced SVG images rather than HTML DOM trees, and did not require web fonts in order to display the math, so the results could be made self-contained. MathJax version 3 includes the CommonHTML and SVG output jax, but has dropped the older, slower HTML-CSS output format.

MathJax 2 also included an output format that produced MathML for those browsers that support it. Since only Firefox and Safari currently implement MathML rendering (with no support in IE, Edge, or Chrome), and because MathJax can’t control the quality or coverage of the MathML support in the browser, MathJax version 3 has dropped the NativeMML output format for now. Should the browser situation improve in the future, it could be added again. See MathML Support for more on this, and for an example of how to implement MathML output yourself.

There are few changes within the supported input and output jax, as described below:

### Input Changes

There are two changes in the TeX input jax that can affect backward compatibility with existing TeX content in your pages.

The first concerns the `\color` macro; in version 2, `\color` is a non-standard in that it takes two arguments (the color an the math to be shown in that color), while the authentic LaTeX version is a switch that changes the color of everything that follows it. The LaTeX-compatible one was available as an extension. In version 3, both versions are extensions (see ), with the LaTeX-compatible one being autoloaded when `\color` is first used. See the color and colorv2 extensions for more information, and how to configure MathJax to use the original version-2 `\color` macro.

The other incompatibility is that the names of some extensions have been changed in version 3. For example, AMScd in version 2 is now amscd in version 3. This means that you need to use `\require{amscd}` rather than `\require{AMScd}` to load the CD environment. In order to support existing content that uses `\require`, you can use the code in the Version 2 Compatibility Example section below.

Some other changes include:

- The autoload-all extension has been rename autoload, and is more flexible and configurable than the original.

- There are two new extensions, braket and physics.

- The configuration options for controlling the format of equation numbers have been moved to an extension; see the tagformat documentation for details.

- The `useMathMLspacing` options for the various input jax have been moved to the output jax instead, as the `mathmlSpacing` option.

- The `processEscapes` option for the tex2jax preprocessor (now for the TeX input jax) had a default value of `false` in version 2, but has default value `true` in version 3.

- The functionality of the MathChoice extension has been moved to the base TeX package.

- The non-standard `UPDIAGONALARROW` and `ARROW` notations have been removed from the `menclose` element. These have been replaced by the standard `northeastarrow` notation.

### Output Changes

There are several important changes to the output jax in version 3, and several things that aren’t yet implemented, but will be in a future version. One such feature is linebreaking, which hasn’t been ported to version 3 yet. Another is that only the MathJax TeX font is currently available in version 3. See Not Yet Ported to Version 3 for a list of features that are still being converted.

In addition, there a few other changes of importance:

- There are no more image fonts. These were for use with the HTML-CSS output jax, and since that is not included in MathJax version 3, neither are the image fonts. Since those took up a lot of disk space, this should make locally hosted MathJax installations smaller.

- For expressions with equation numbers, the SVG output jax now has these expressions float with the size of the container element, just like they do in HTML output. This was not the case in version 2, so this is an important improvement for dynamic pages.

- The font used for characters that aren’t in the font used by MathJax used to be controlled by the `undefinedFont` configuration parameter in version 2, but in version 3, you should use CSS to set this instead. For example,

      mjx-container mjx-utext {
        font-family: my-favorite-font;
      }
      mjx-container svg text {
        font-family: my-favorite-font;
      }

  would select the `my-favorite-font` to be used for unknown characters. The first declaration is for the CommonHTML output, and the second for the SVG output. Once advantage of this approach is that you can specify the CSS separately for each variant; e.g.,

      mjx-container mjx-utext[variant="sans-serif"] {
        font-family: my-sans-serif-font;
      }
      mjx-container svg text[data-variant="sans-serif"] {
        font-family: my-sans-serif-font;
      }

  would set the font to use for characters that aren’t in the MathJax fonts and that have requested the sans-serif variant.

- Version 3 only implements the CommonHTML and SVG output jax. The original HTML-CSS output jax has been dropped, a has the NativeMML. The PreviewHTML and PlainSource output jax have not been ported to version 3, though they may be in the future, if there is interest.

## No Longer Applies to Version 3

A number of version 2 features have been removed as part of the redesign of MathJax version 3. These are described below.

- In version 3, MathJax no longer updates the page in small “chunks”, but instead updates the page as a whole (a future version may include an extension that updates in smaller pieces). This has an impact on a number of version 2 features. First, because there is no incremental update, the MathJax message bar (usually in the lower left corner) that indicated the progress of the typesetting is no longer needed, and is not part of MathJax version 3. Of course, the configuration options that control it have also been removed, as have the options for equation chunking (that controlled how many equations to process between screen updates.

- Similarly, since the page updating is done all at once, there is no need for the math preview versions that were displayed while the equations where being typeset. So the fast-preview extension and PreviewHTML output jax have been removed, along with the configuration options for them.

- The PlainSource output jax has not be ported to version 3, though it may be in the future; it can be handled in other ways in version 3. As mentioned above, the NativeMML has been dropped from version 3, though it is not hard to implement a replacement if you want.

- The autobold TeX extension is no longer available in version 3, and is unlikely to be ported in the future.

- The mhchem TeX extension in version 2 came in two forms: the original extension that didn’t match the LaTeX implementation perfectly, and a rewrite by the author of the original LaTeX package that made it compatible with LaTeX. The legacy version could be selected by a configuration option. This is no longer possible in version 3 (the legacy version is no longer provided).

- The handle-floats extension for HTML output has been removed, as its functionality is now part of the standard CommonHTML output.

- The jsMath2jax preprocessor has been dropped. This was used to help bridge jsMath users to MathJax, but since it has been a decade since MathJax was introduced, the need for jsMath conversion should be very small at this point.

- The MatchWebFonts extension is no longer available. This was sometimes needed for HTML-CSS output, which relied on the fonts being in place when it ran. The CommonHTML output is less susceptible to font issues, and this is no longer necessary.

- The FontWarnings extension is no longer available, since it was for the HTML-CSS output jax, which is not part of MathJax version 3.

- The HelpDialog extension is not included in version 3. Its functionality is incorporated into the ui/menu directly.

- The toMathML extension is no longer provided in version 3. Instead, you can use `MathJax.startup.toMML()` if you are using MathJax components, or can use the `SerializedMMLVisitor` object if you are calling MathJax modules directly.

- The configuration blocks no longer allow the `style` option that were available in version 2. Instead, you should use CSS stylesheets and CSS style files directly.

- Synchronization with MathJax in version 2 was handled via queues, signals, and callbacks. In version 3, these have been replaced by ES6 promises. See Synchronizing your code with MathJax for more details.

## Not Yet Ported to Version 3

As MathJax 3 is still a work in progress, not all of the version 2 features have been converted to the new code base yet, though we hope to include them in version 3 in a future release. Among the most important ones are the following.

- Currently, automatic line breaking support is missing from version 3. This is a key feature to be included in a future release.

- The MathJax v3 output jax currently only support one font, the MathJax TeX fonts. Improved font support is an important goal for version 3, and this is one of the next features to be addressed. We will be rebuilding the fonts used for MathJax, and making additional web fonts available in a future release. We also plan to make the tools used for creating the necessary font data available for use in porting your own fonts for use with MathJax.

- The localization mechanism available in version 2 has not yet been incorporated into version 3, so currently MathJax v3 is available only in English. This is an important feature that will be added to MathJax v3 in a future release.

- The begingroup and mediawiki-texvc TeX extensions haven’t been ported to version 3 yet, but should be in the future.

- The auto-collapse assistive extension is not yet available for version 3. If there is enough interest, that will also be ported to the new code base.

## Contextual Menu Changes

The contextual menu has been reorganized to make it easier to access some functions, and to add new ones. One major new features is the Copy to Clipboard submenu, which mirrors the Show Math As menu, but sends the output to the clipboard rather than displaying it on screen. This is a feature that has been requested for a long time, and we are pleased to be able to offer it in version 3.

There is also a new Reset to defaults item that resets all the saved settings to their original values (effectively clearing any custom settings).

The contextual menu now stores its data using the `localStorage` object in the browser, rather than using cookies like version 2 does. This should be more efficient and more secure, but does mean older browsers may not be able to save their settings from session to session (if they don’t support `localStorage`).

The accessibility menu options are now built into the contextual menu, so there is no longer an accessibility-menu extension. They also have been reorganized in the menu to make it easier to access the more important features. The auto-collapse extension has not yet been ported to version 3, however. The equation explorer has been expanded and improved; see Accessibility Features for details.

Finally, the `showMathMenu` and `showMathMenuMSIE` options have been removed. The need for separate handling of the menu in IE is no longer applicable, and you control whether the contextual menu is attached to the typeset mathematics using the `enableMenu` property of the `options` block of the MathJax configuration (see the Contextual Menu Options documentation).

## MathJax in Node

Version 2 of MathJax was designed to work in a browser, and relied heavily on the presence of the browser window, document, DOM, and other browser-specific objects. Using MathJax on a server to pre-process mathematics (e.g., to convert a TeX string to an SVG image, for example), was not easy in version 2. The mathjax-node <https://github.com/mathjax/mathjax-node> project made that possible, but required a completely different way of interacting with MathJax, and was not as easy to use or as reliable as we would have liked.

Version 3 has server-side use as an important use-case to support, and so it is possible to use MathJax in a node application in essentially the same way as in a browser, with only a few minor adjustments to the configuration to allow for that. This should make it much easier to use MathJax on a server, as it will work the same there as for your web-based applications. It is also possible to link to MathJax at a lower level and access the MathJax modules directly. See the section on using MathJax in node, and the MathJax API for more information on these possibilities.

## Version 2 Compatibility Example

The following example causes the `\color` macro to be the original one from version 2, and sets up the `\require` macro to translate the old package names into the new ones. This should make MathJax v3 handle existing content properly.

Be sure to convert your version-2 configuration to a version-3 one via the conversion tool that we provide.

    <script>
    MathJax = {
      startup: {
        //
        //  Mapping of old extension names to new ones
        //
        requireMap: {
          AMSmath: 'ams',
          AMSsymbols: 'ams',
          AMScd: 'amscd',
          HTML: 'html',
          noErrors: 'noerrors',
          noUndefined: 'noundefined'
        },
        ready: function () {
          //
          //  Replace the require command map with a new one that checks for
          //    renamed extensions and converts them to the new names.
          //
          var CommandMap = MathJax._.input.tex.SymbolMap.CommandMap;
          var requireMap = MathJax.config.startup.requireMap;
          var RequireLoad = MathJax._.input.tex.require.RequireConfiguration.RequireLoad;
          var RequireMethods = {
            Require: function (parser, name) {
              var required = parser.GetArgument(name);
              if (required.match(/[^_a-zA-Z0-9]/) || required === '') {
                throw new TexError('BadPackageName', 'Argument for %1 is not a valid package name', name);
              }
              if (requireMap.hasOwnProperty(required)) {
                required = requireMap[required];
              }
              RequireLoad(parser, required);
            }
          };
          new CommandMap('require', {require: 'Require'}, RequireMethods);
          //
          //  Do the usual startup
          //
          return MathJax.startup.defaultReady();
        }
      },
      tex: {
        autoload: {
          color: [],          // don't autoload the color extension
          colorv2: ['color'], // do autoload the colorv2 extension
        }
      }
    };
    </script>
    <script id="MathJax-script" async
     src="https://cdn.jsdelivr.net/npm/mathjax@3/es5/tex-chtml.js"></script>

This uses the `tex-chtml.js` combined component, so change this to whichever one you want.

If your website uses the MathJax API to queue typeset calls via

    MathJax.Hub.Queue(['Typeset', MathJax.Hub]);

for example, these calls will need to be converted to use the MathJax 3 API. You may be able to use the following code to patch into MathJax version 3, which provides implementations for `MathJax.Hub.Typeset()`, and `MathJax.Hub.Queue()`. It also flags usages of `MathJax.Hub.Register.StartupHook()` and the other hook-registering commands, and that you have converted your `MathJax.Hub.Config()` and `x-mathjax-config` scripts to their version 3 counterparts (use the conversion tool).

Add the following lines right after the `new CommandMap()` call in the code above:

    //
    // Add a replacement for MathJax.Callback command
    //
    MathJax.Callback = function (args) {
      if (Array.isArray(args)) {
        if (args.length === 1 && typeof(args[0]) === 'function') {
          return args[0];
        } else if (typeof(args[0]) === 'string' && args[1] instanceof Object &&
                  typeof(args[1][args[0]]) === 'function') {
          return Function.bind.apply(args[1][args[0]], args.slice(1));
        } else if (typeof(args[0]) === 'function') {
          return Function.bind.apply(args[0], [window].concat(args.slice(1)));
        } else if (typeof(args[1]) === 'function') {
          return Function.bind.apply(args[1], [args[0]].concat(args.slice(2)));
        }
      } else if (typeof(args) === 'function') {
        return args;
      }
      throw Error("Can't make callback from given data");
    };
    //
    // Add a replacement for MathJax.Hub commands
    //
    MathJax.Hub = {
      Queue: function () {
        for (var i = 0, m = arguments.length; i < m; i++) {
           var fn = MathJax.Callback(arguments[i]);
           MathJax.startup.promise = MathJax.startup.promise.then(fn);
        }
        return MathJax.startup.promise;
      },
      Typeset: function (elements, callback) {
         var promise = MathJax.typesetPromise(elements);
         if (callback) {
           promise = promise.then(callback);
         }
         return promise;
      },
      Register: {
         MessageHook: function () {console.log('MessageHooks are not supported in version 3')},
         StartupHook: function () {console.log('StartupHooks are not supported in version 3')},
         LoadHook: function () {console.log('LoadHooks are not supported in version 3')}
      },
      Config: function () {console.log('MathJax configurations should be converted for version 3')}
    };
    //
    //  Warn about x-mathjax-config scripts
    //
    if (document.querySelector('script[type="text/x-mathjax-config"]')) {
      throw Error('x-mathjax-config scripts should be converted to MathJax global variable');
    }

With this you may be able to get away with using your existing version 2 code to interact with version 3. But if not, either a more sophisticated compatibility module will be needed, or better yet, convert to the new version 3 API.