Preamble option for KaTex

[Edenharder]

I would be nice if we can define extra commands for KaTex, then we do not need to type the complicated expression each time. It is indeed possible in KaTex, for example this issue. There is also a similar plugin for Obsidian.

[MinusGix]

I implemented a basic version (on local copy of Logseq) which just allows the user to set the macros field for katex.render:

(defn render!
  [state]
  (let [[id s display?] (:rum/args state)]
    (let [macros (clj->js (get (state/get-config) :katex-macros {}))]
      (try
        (js/katex.render s (gdom/getElement id)
                         #js {:displayMode display?
                              :throwOnError false
                              :strict false
                              :macros macros})
        (catch js/Error e
          (js/console.error e))))))

but this requires the usage to be like (in their config.edn:

:katex-macros { 
    "\\if" "\\ \\text{if}\\ "
}

but that is somewhat unpleasant.
One issue with this approach is that simply setting the macros field to an object (even an empty object) makes so it is modified whenever Katex renders \gdef\somecommand{2 + 2} (see: https://katex.org/docs/options.html). This would actually be nice by itself but it persists across different pages, and all pages aren't rendered at the same time so you can run into situations where a macro is \gdef'd in a file you haven't viewed yet and so it doesn't render in another file. I don't think this is too major, but it could be a source of confusion.

The option that is closer to the issue linked is to have some special file (ex: katex-macros.tex) that is read and has the contents inserted at the top of the 'root' page (not sure what the terminology is in this project, but it could probably be 'displayed' once by putting it outside the main editing area). This would require globalGroup: true, but I think that could be potentially be avoided in-general by only using globalGroup on that render specifically.

[MinusGix]

I'm curious as to why this was closed? It doesn't appear to have been added or an alternative created, unless I'm missing something.

[cnut1648]

Yeah I am also pretty interested in this feature, and I wonder if there is a more elegant solution.

[Drekin]

+1 for such feature. It would be much nice to write e.g. \rng(f ∘ g) instead of \operatorname{rng}(f \circ g).

[kalaspa]

You can add Katex macros directly in your logseq/custom.js, with the following code:

function whenAvailable(name, callback) {
    var interval = 10; // ms
    window.setTimeout(function() {
        if (window[name]) {
            callback(window[name]);
        } else {
            whenAvailable(name, callback);
        }
    }, interval);
}


whenAvailable("katex", function(t) {
    // Put your macros below, key will be replaced by the corresponding macro
    katex.__defineMacro(key, macro);
});

[cnut1648]

Thanks @kalaspa ! That works. Just posting some examples of how to use it

whenAvailable("katex", function(t) {
    // Put your macros below, key will be replaced by the corresponding macro
    katex.__defineMacro("\\E", "\\mathbb{E}");
    katex.__defineMacro("\\pdv", "\\dfrac{\\partial #1}{\\partial #2}");
    katex.__defineMacro("\\dv", "\\dfrac{d #1}{d #2}");
});

[Drekin]

Thanks! This is much cleaner that hacking directly into katex.min.js.

[honzaprevratil]

@cnut1648 Hi, I tried the putting your snippet combined with the function whenAvailable posted by @kalaspa but it's not working for me. Do you have any ideas, what to do to fix it?

[cnut1648]

Hi @honzaprevratil I still use the same code and the macro works for me. When I open the logseq sometimes there is a popup asking if I allow logseq to run custom.js. Only when I click yes will logseq use the macro. The only issue is that I do not know how to trigger the popup.