Replace all text in a webpage with random characters

replace-text.js

"use strict";

function isExcluded(elm) {
    if (elm.tagName == "STYLE") {
        return true;
    }
    if (elm.tagName == "SCRIPT") {
        return true;
    }
    if (elm.tagName == "NOSCRIPT") {
        return true;
    }
    if (elm.tagName == "IFRAME") {
        return true;
    }
    if (elm.tagName == "OBJECT") {
        return true;
    }
    return false
}

function traverse(elm) {
    if (elm.nodeType == Node.ELEMENT_NODE || elm.nodeType == Node.DOCUMENT_NODE) {

        // exclude elements with invisible text nodes
        if (isExcluded(elm)) {
            return
        }

        for (let childNode of elm.childNodes) {
            // recursively call to traverse
            traverse(childNode);
        }

    }

    if (elm.nodeType == Node.TEXT_NODE) {

        // exclude text node consisting of only spaces
        if (elm.nodeValue.trim() === "") {
            return
        }

        // Pass true as second parameter to replace with letters
        elm.nodeValue = replaceText(elm.nodeValue);
    }
}

function replaceText(text, fillAlphabet = false) {
    let out = [];

    for (let char of text?.split('')) {
        if (char === ' ') {
            out.push(char);
        } else {
            const replacement = fillAlphabet ? generateRandomLetter() : 'x';

            if (/[a-z]/.test(char)) {
                out.push(replacement);
            } else {
                out.push(replacement.toUpperCase());
            }
        }
    }

    return out.join('');
}

function generateRandomLetter() {
    const alphabet = 'abcdefghijklmnopqrstuvwxyz';

    return alphabet[Math.floor(Math.random() * alphabet.length)]
}

traverse(document);