"Has bad words?" script for Neopets textareas [needs word list!]

has-bad-words.js

const ALL_BAD_WORDS = [
    // Except, like, replace this with the actual list of words.
    "uncle",
    "grape"
];

/** Return a list of bad words that appear in the given text. */
function findBadWords(text) {
    return ALL_BAD_WORDS.filter(badWord => text.includes(badWord));
}

/** Given a textarea, check for bad words. If so, log them & style the box. */
function checkTextarea(textarea) {
    const badWords = findBadWords(textarea.value);
    const hasBadWords = badWords.length > 0;

    textarea.classList.toggle("has-bad-words", hasBadWords);

    for (const badWord of badWords) {
        console.log("Text contains the following bad word:", badWord);
    }
}

/** Add "has-bad-words" CSS class to the document, for use in checkTextarea. */
function addCSS() {
    // Add the red-background styles as a CSS class, so we can quickly toggle
    // it as the user types, without polluting local styles.
    const node = document.createElement("style");
    node.type = "text/css";
    node.innerHTML = `
        /* Injected by Neopets has-bad-words bookmarklet. */
        .has-bad-words {
            background: #faa !important;
        }
    `;
    document.body.appendChild(node);
}

/** Handle any change event on the page. If it's for a textarea, check it. */
function handleChange(event) {
    if (event.target.tagName === "TEXTAREA") {
        checkTextarea(event.target);
    }
}

/** Add global event listeners for all textarea change events. */
function addListeners() {
    // Listen for all change and keyup events, to catch keyboard & non-keyboard
    // changes. This will trigger some false positives (i.e. key presses not in
    // textareas), but `handleChange` quickly checks and ignores that case.
    document.addEventListener("change", handleChange, true);
    document.addEventListener("keyup", handleChange, true);
}

/** Check all textareas proactively, instead of waiting for them to change. */
function checkAllTextareas() {
    const textareas = document.querySelectorAll("textarea");
    for (const textarea of textareas) {
        checkTextarea(textarea);
    }
}

// To start up, add the CSS, add the event listeners, and check all textareas
// in case they already contain bad words.
addCSS();
addListeners();
checkAllTextareas();