Structural Visual Anchors for PressReader

A lightweight userscript that subtly highlights English function words while reading on PressReader.
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// ==UserScript==
// @name         Structural Visual Anchors for PressReader
// @namespace    http://tampermonkey.net/
// @version      1.0.0
// @match        *://*.pressreader.com/*
// @description  A lightweight userscript that subtly highlights English function words while reading on PressReader.
// @author       cccccc
// @grant        none
// @run-at       document-end
// @license MIT
// ==/UserScript==

(function () {
    'use strict';

    const targetWords =
        /\b(a|an|the|in|on|at|of|to|for|with|by|from)\b/gi;

    const style = document.createElement("style");
    style.textContent = `
        ::highlight(function-word-anchor) {
            background: transparent !important;
            color: inherit !important;
            text-decoration: underline dotted #888;
            text-underline-offset: 2px;
        }
    `;
    document.head.appendChild(style);

    const highlight = new Highlight();
    CSS.highlights.set("function-word-anchor", highlight);

    function scan() {

        highlight.clear();

        const paragraphs = document.querySelectorAll(`
            p.article-text,
            p.article-text.trimmed
        `);

        paragraphs.forEach(p => {

            const walker = document.createTreeWalker(
                p,
                NodeFilter.SHOW_TEXT
            );

            let node;

            while ((node = walker.nextNode())) {

                const text = node.nodeValue;

                targetWords.lastIndex = 0;

                let match;

                while ((match = targetWords.exec(text))) {

                    const range = new Range();

                    range.setStart(node, match.index);
                    range.setEnd(node, match.index + match[0].length);

                    highlight.add(range);
                }
            }

        });

    }

    let timer;

    const observer = new MutationObserver(() => {

        clearTimeout(timer);

        timer = setTimeout(scan, 200);

    });

    observer.observe(document.body, {
        childList: true,
        subtree: true
    });

    window.addEventListener("load", scan);

    setTimeout(scan, 1000);
    setTimeout(scan, 2500);
    setTimeout(scan, 5000);

})();