Memory leak when linking to MathJax directly #3591

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1. dpvc commented on Jul 16, 2026

   

   dpvc

   on Jul 16, 2026

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   Thanks for your report. I am able to verify the problem you are seeing, though I haven't fully diagnosed it yet. The majority of the problem seems to be due to the large number of instances of the CHTML output jax that are involved here, so I suspect that it is the font data that is causing the problem. I will have to track it down, but wanted to give you some options in the meantime.

   The /@jajaperson+rehype-mathjax package is creating the input and output jax and the MathDocument for each of the 1,900 documents that you process. You also create the DOM adaptor and register/unregister the HTML handler for each document. Not all of that is necessary to do each time, and that is contributing to the memory problem. It also degrades the performance, particularly recreating the output jax, which has to process the font data each time as it creates its own FontData instance.

   Fortunately, the output jax can be reused, which eliminates both the performance hit, as well as reducing the memory usage. You also only need to create the DOM adaptor and register the HTML handler once up front.

   Here are some changes that I think will reduce the problem that you are having:

   In the create-renderer.js file, add

   const adapter = liteAdapter();
   const handler = registerHtmlHandler(adapter);

   right after all the import commands, and then remove

     /** @type {HtmlHandler<LiteElement | LiteText, LiteText, LiteDocument>} */
   let handler

   from the createRenderer() function. Also, remove

         const adapter = liteAdapter()
         handler = registerHtmlHandler(adapter)

   from the register() function within it. Finally, replace

         mathjax.handlers.unregister(handler)

   in the unregistered() function with

         const jax = document.outputJax;
         jax.reset();
         if (jax.chtmlStyles) jax.chtmlStyles = null;
         if (jax.svgStyles) jax.svgStyles = null;

   Then in chtml.js, add

   let chtml;

   at the top, and replace

     return createRenderer(options, new Chtml(options.chtml))

   with

     chtml ??= new Chtml(options.chtml);
     return createRenderer(options, chtml);

   Do the similar thing in svg.js.

   These changes will allow you to reuse the output jax, rather than re-instantiating over and over again. If you are not defining new macros, it would be possible to do something similar with the input jax. Even the mathjax.document() value could be reused in that case. It looks like you are only used \def to create \fCenter as \vdash, and one other macro. Those could be added to your main macro list, or, since you aren't redefining any standard macros, you could just reuse the input jax as it is, as those two macros won't interfere with anything if they are held over from one to the next. That gives me pretty stable memory usage; I think you should find the same.
2. dpvc

   added

   AcceptedIssue has been reproduced by MathJax teamIssue has been reproduced by MathJax team

   v4

   Investigate

   on Jul 16, 2026
3. jajaperson

   added a commit that references this issue on Jul 17, 2026

   Improve performance

   ...

   9da4cbe
4. jajaperson commented on Jul 17, 2026

   

   jajaperson

   on Jul 17, 2026

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   Thanks, I have followed your suggestion and this has completely fixed the issue for me, memory usage is down to about 181 kB and build time has halved. I am happy if you close this, but maybe you still want to investigate why re-initializing MathJax caused a problem.