Notion.so Custom Domain + Inline LaTeX Rendering

worker.js

const MY_DOMAIN = "YOUR_DOMAIN"
const START_PAGE = "URL_TO_NOTION_LANDING_PAGE"

addEventListener('fetch', event => {
    event.respondWith(fetchAndApply(event.request))
})

const corsHeaders = {
    "Access-Control-Allow-Origin": "*",
    "Access-Control-Allow-Methods": "GET, HEAD, POST,PUT, OPTIONS",
    "Access-Control-Allow-Headers": "Content-Type",
}

function handleOptions(request) {
    if (request.headers.get("Origin") !== null &&
        request.headers.get("Access-Control-Request-Method") !== null &&
        request.headers.get("Access-Control-Request-Headers") !== null) {
        // Handle CORS pre-flight request.
        return new Response(null, {
            headers: corsHeaders
        })
    } else {
        // Handle standard OPTIONS request.
        return new Response(null, {
            headers: {
                "Allow": "GET, HEAD, POST, PUT, OPTIONS",
            }
        })
    }
}

async function fetchAndApply(request) {
    if (request.method === "OPTIONS") {
        return handleOptions(request)
    }
    let url = new URL(request.url)
    let response
    if (url.pathname.startsWith("/app") && url.pathname.endsWith("js")) {
        // skip validation in app.js
        response = await fetch(`https://www.notion.so${url.pathname}`)
        let body = await response.text()
        try {
            response = new Response(body.replace(/www.notion.so/g, MY_DOMAIN).replace(/notion.so/g, MY_DOMAIN), response)
            response.headers.set('Content-Type', "application/x-javascript")
            console.log("get rewrite app.js")
        } catch (err) {
            console.log(err)
        }

    } else if ((url.pathname.startsWith("/api"))) {
        // Forward API
        response = await fetch(`https://www.notion.so${url.pathname}`, {
            body: request.body, // must match 'Content-Type' header
            headers: {
                'content-type': 'application/json;charset=UTF-8',
                'user-agent': 'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/73.0.3683.103 Safari/537.36'
            },
            method: "POST", // *GET, POST, PUT, DELETE, etc.
        })
        response = new Response(response.body, response)
        response.headers.set('Access-Control-Allow-Origin', "*")
    } else if (url.pathname === `/`) {
        // 301 redrict
        let pageUrlList = START_PAGE.split("/")
        let redrictUrl = `https://${MY_DOMAIN}/${pageUrlList[pageUrlList.length - 1]}`
        return Response.redirect(redrictUrl, 301)
    } else {
        response = await fetch(`https://www.notion.so${url.pathname}`, {
            body: request.body, // must match 'Content-Type' header
            headers: request.headers,
            method: request.method, // *GET, POST, PUT, DELETE, etc.
        })
        response = new Response(response.body, response)
    }

    response.headers.delete("Content-Security-Policy")
    return new HTMLRewriter().on('body', new ElementHandler()).transform(response)
    return response
}

class ElementHandler {
    element(element) {
        element.append(`
<script src=https://cdn.jsdelivr.net/npm/katex@0.11.1/dist/katex.min.js></script>
<script src=https://cdn.jsdelivr.net/npm/katex@0.11.1/dist/contrib/auto-render.min.js></script>
<script type="text/javascript">
    // right-padding for inline math mode
    var style = document.createElement('style');
    style.innerHTML = '.katex{padding-right:0!important;}';
    document.head.appendChild(style);
    
    // declare/init vars
    let timer; // timer identifier
    let startUpWaitTime = 3000; // ms after startup (adjust as needed)
    let pageChangeWaitTime = 1500; // ms after page changed (adjust as needed)
    let backupRender;
    let backupRenderWaitTime = 6000;
    
    // render inline LaTeX
    function renderInlineLaTeX() {
      renderMathInElement(document.body, {
        delimiters: [
          // LaTeX delimiters (uncomment/add as needed)
          { left: "$$", right: "$$", display: true },
          // { left: "\\[", right: "\\]", display: true  },
          // { left: "\\(", right: "\\)", display: false },
          { left: "$", right: "$", display: false }
        ]
      });
      console.log("Inline LaTeX is rendered.");
    }
    
    let url = window.location.href;

    ['click','popstate'].forEach( evt =>
        window.addEventListener(evt, function () {
            requestAnimationFrame(()=>{
                if (url !== location.href) {
                    renderOnPageChange();
                }
                url = location.href;
            });
        }, true)
    );

    function renderOnLoad() {
        console.log("Rendering inline LaTeX on startup...");
        clearTimeout(timer);
        timer = setTimeout(renderInlineLaTeX, startUpWaitTime);
        backupRendering();
    }

    function renderOnPageChange() {
        console.log("Rendering inline LaTeX on navigation...");
        clearTimeout(timer);
        timer = setTimeout(renderInlineLaTeX, pageChangeWaitTime);
        backupRendering();
    }

    function backupRendering() {
        clearTimeout(backupRender);
        backupRender = setTimeout(function() {
            console.log("Rerendering just in case...");
            renderInlineLaTeX();
        }, backupRenderWaitTime);
    }

    // on startup...
    window.addEventListener("DOMContentLoaded", renderOnLoad);
</script>
`, {
            html: true
        })
    }
}