y_u_no_chat_nice.js

(function() {
    'use strict';

    /**
     * Modifications to perform (processed in order)
     *
     * @type {Function[]}
     */
    const modifications = [
        (text) => text.replace(/!+/g, '!'),
    ];

    /**
     * Root element to watch for changes in descendants
     *
     * @type {Element}
     */
    const container = document.body;

    /**
     * Execute the replacement operations against a CharacterData node
     *
     * @param {CharacterData} node
     */
    function process_text_node(node)
    {
        let fixed = node.nodeValue;

        modifications.forEach(function(callback) {
            fixed = callback(fixed);
        });

        if (node.nodeValue !== fixed) {
            node.nodeValue = fixed;
        }
    }

    /**
     * Recursively walk the children of an Element and process any CharacterData nodes found in its descendants
     *
     * @param {Element} element
     */
    function walk_element(element)
    {
        let node = element.firstChild;

        while (node) {
            if (node instanceof CharacterData) {
                process_text_node(node);
            } else if (node instanceof Element) {
                walk_element(node);
            }

            node = node.nextSibling;
        }
    }

    /**
     * Process an array of MutationRecord objects for added or updated character data
     *
     * @param {MutationRecord[]} mutations
     */
    function process_mutations(mutations)
    {
        mutations.forEach(function(mutation) {
            switch (mutation.type) {
                case 'childList':
                    Array.prototype.forEach.call(mutation.addedNodes, function(node) {
                        if (node instanceof CharacterData) {
                            process_text_node(node);
                        } else if (node instanceof Element) {
                            walk_element(node);
                        }
                    });
                    break;

                case 'characterData':
                    process_text_node(mutation.target);
                    break;
            }
        });
    }

    // Fix existing page text
    walk_element(container);

    // Register the mutation observer to process future changes on the page
    (new MutationObserver(process_mutations)).observe(container, {
        childList: true,
        subtree: true,
        characterData: true,
    });
}());