Notion - Inline Math for the Desktop App (credit https://www.notion.so/Notion-Hacks-27b92f71afcd4ae2ac9a4d14fef0ce47)

inlinemath-userscript.js

// ==UserScript==
// @name Inline Math for Notion.so
// @homepageURL https://www.notion.so/evertheylen/Notion-Inline-Math-9c5047a4e7c84643848b3630db8d5a5e
// @version 0.2.1
// @match https://www.notion.so/*
// @grant GM_addStyle
// @require https://cdn.jsdelivr.net/npm/[email protected]/dist/katex.js
// ==/UserScript==

// Instructions for use:
//   - Make sure you have at least one normal math block on your page
//   - Use inline code starting with "math:". For example: `math: f(x) = x^2`
//   - Press F2 to rerender all inline math. You can of course change the shortcut in the code below.
//   - The inline math will revert to inline code when the block becomes active.

const subscript = /_(?!{)(.+?)(?:_|(\^|$| ))/g
const superscript = /\^(?!{)(.+?)(?:\^|(_|$| ))/g

GM_addStyle(`
.notion-frame span .katex {
    padding-right: 0 !important;
    font-size: 1.3em;
}
`)

function rerender_all(e) {
    document.querySelectorAll("body").innerHTML = "";
    var code = document.querySelectorAll('span[style*="monospace"]');
    code.forEach(function(el) {
        if (document.activeElement.contains(el)) {
            if (e.key != "F2") {
                return;
            }
        }
        var s = el.textContent;
        if (s.startsWith("math:")) {
            el.style.color = null;
            el.style.background = null;
            s = s.slice(5).trim();
            katex.render(s, el, {throwOnError: true, font: "mathit"});
        } else if (s.startsWith(",")) {
            el.style.color = null;
            el.style.background = null;
            s = "\\mathrm{" + s.slice(1).trim() + "}";

            var match;
            while (match = s.match(subscript)) {
                s = s.replace(subscript, "_{$1}$2");
            }
          
            while (match = s.match(superscript)) {
                s = s.replace(superscript, "^{$1}$2");
            }        

            katex.render(s, el, {throwOnError: true, font: "mathit"});
        } else if (s.startsWith("$")) {
            el.style.color = null;
            el.style.background = null;
            s = s.slice(1).trim();
            katex.render(s, el, {throwOnError: true, font: "mathit"});
        }
    });
}

function rerender() {
    rerender_all({key: "discard"});
    setTimeout(rerender, 500);
}
setTimeout(rerender, 5000);

window.addEventListener("mousedown", rerender_all);
window.addEventListener("keydown", rerender_all, true);

inlinemath.js

const subscript = /_(?!{)(.+?)(?:_|(\^|$| ))/g
const superscript = /\^(?!{)(.+?)(?:\^|(_|$| ))/g

window.onload = function(e) {
    loadJS(
        "https://cdn.jsdelivr.net/npm/[email protected]/dist/katex.min.js",
        function() {
            rerender_all();
        },
        document.body
    );

    let customCSS = document.createElement("style");
    customCSS.innerHTML = `.notion-frame span .katex {
            padding-right: 0 !important;
            font-size: 1.3em;
        }`;
    document.getElementsByTagName("head")[0].appendChild(customCSS);
};

var loadJS = function(url, implementationCode, location) {
    //url is URL of external file, implementationCode is the code
    //to be called from the file, location is the location to
    //insert the <script> element

    var scriptTag = document.createElement("script");
    scriptTag.src = url;

    scriptTag.onload = implementationCode;
    scriptTag.onreadystatechange = implementationCode;

    location.appendChild(scriptTag);
};

function rerender_all(e) {
    document.querySelectorAll("body").innerHTML = "";
    var code = document.querySelectorAll('span[style*="monospace"]');
    code.forEach(function(el) {
        if (document.activeElement.contains(el)) {
            if (e.key != "F2") {
                return;
            }
        }
        var s = el.textContent;
        if (s.startsWith("math:")) {
            el.style.color = null;
            el.style.background = null;
            s = s.slice(5).trim();
            katex.render(s, el, {throwOnError: true, font: "mathit"});
        } else if (s.startsWith(",")) {
            el.style.color = null;
            el.style.background = null;
            s = "\\mathrm{" + s.slice(1).trim() + "}";

            var match;
            while (match = s.match(subscript)) {
                s = s.replace(subscript, "_{$1}$2");
            }
          
            while (match = s.match(superscript)) {
                s = s.replace(superscript, "^{$1}$2");
            }        

            katex.render(s, el, {throwOnError: true, font: "mathit"});
        } else if (s.startsWith("$")) {
            el.style.color = null;
            el.style.background = null;
            s = s.slice(1).trim();
            katex.render(s, el, {throwOnError: true, font: "mathit"});
        }
    });
}

function rerender() {
    rerender_all({key: "discard"});
    setTimeout(rerender, 500);
}
setTimeout(rerender, 5000);

window.addEventListener("mousedown", rerender_all);
window.addEventListener("keydown", rerender_all, true);

patcher.sh

( cd /Applications/Notion.app/Contents/Resources; asar extract app.asar app )

# cp inlinemath.js /Applications/Notion.app/Contents/Resources/app/renderer/inlinemath.js

# sed -i '' 's/<\/head>/<script src="inlinemath.js"><\/script><\/head>/g' /Applications/Notion.app/Contents/Resources/app/renderer/index.html

echo "\n" >> /Applications/Notion.app/Contents/Resources/app/renderer/preload.js
cat inlinemath.js >> /Applications/Notion.app/Contents/Resources/app/renderer/preload.js

When would Notion load files from local? It seems like for me Notion is always using the online app.js. Would it be possible to patch content in app.js?

The desktop Notion app loads file contents from the app.azar. By editing app.azar, we can edit the code which loads the Notion webpage (it's not just a frame around the web app, there's also a little bit of wrapper code). @alanzchen

Can someone please walk me through installing this? I have no idea what to do, thanks.