improved-crowdcast-ux/content.js

function setChatWidth(width) {
    document.querySelector('body').style.setProperty("--chat-width", width + 'px');
}

function setHighlightColor(color) {
    document.querySelector('body').style.setProperty("--highlight-color", color);
}

chrome.storage.onChanged.addListener((changes, areaName) => {
    if ('chatWidth' in changes) {
        setChatWidth(changes.chatWidth.newValue);
    }

    if ('highlightColor' in changes) {
        setHighlightColor(changes.highlightColor.newValue);
    }
});

chrome.storage.sync.get(null, (settings) => {
    if ('chatWidth' in settings) {
        setChatWidth(settings.chatWidth);
    }

    if ('highlightColor' in settings) {
        setHighlightColor(settings.highlightColor);
    }
});

class TabCompletion {
    constructor() {
        this.ownUsernameRegExp = null;
        this.usernames = [];
    }

    setOwnUsername(username) {
        this.ownUsernameRegExp = new RegExp('@?' + username.replace(/[-\/\\^$*+?.()|[\]{}]/g, '\\$&'), 'gi');
    }

    addUsername(username) {
        if (!this.usernames.includes(username)) {
            this.usernames.push(username);
        }
    }

    complete(input, start, symbol, choices) {
        let partial = input.value.substring(start + 1, input.selectionStart).trim();

        if (partial === this[`suggestion_${symbol}`]) {
            partial = this[`partial_${symbol}`];
        } else {
            this[`partial_${symbol}`] = partial;
        }

        const possibilities = choices.filter((choice) => choice.toLowerCase().startsWith(partial.toLowerCase()));

        if (this[`completionIndex_${symbol}`] === undefined || ++this[`completionIndex_${symbol}`] >= possibilities.length) {
            this[`completionIndex_${symbol}`] = 0;
        }

        if (possibilities.length > 0) {
            this[`suggestion_${symbol}`] = possibilities[this[`completionIndex_${symbol}`]].trim();

            input.value = input.value.substring(0, start + 1) + this[`suggestion_${symbol}`] +
                ' ' + input.value.substring(input.selectionStart);
            input.selectionStart = start + this[`suggestion_${symbol}`].length + 2;
            input.selectionEnd = input.selectionStart;
        }
    }

    attempt(input) {
        const at = input.value.lastIndexOf('@', input.selectionStart - 1);
        let colon = input.value.lastIndexOf(':', input.selectionStart - 1);

        // ignore colon at the end of emoji shortname
        if (colon !== -1) {
            const match = emojis.shortnameRegExp.exec(input.value);

            if (match !== null) {
                colon = match.index;
            }
        }

        if (at !== -1 && at > colon) {
            this.complete(input, at, '@', this.usernames);
        } else if (colon !== -1 && colon > at) {
            this.complete(input, colon, ':', emojis.shortnames.map((s => s + ':')));
        } else {
            return false;
        }

        return true;
    }
}

const tabCompletion = new TabCompletion();

(new MutationObserver((mutationsList, observer) => {
    for (let mutation of mutationsList) {
        for (let node of mutation.addedNodes) {
            if (node.nodeType === 1 && (username = node.querySelector('span.user-name')) !== null) {
                (new MutationObserver((mutationsList, observer) => {
                    for (let mutation of mutationsList) {
                        tabCompletion.setOwnUsername(mutation.target.data.trim());
                    }
                })).observe(username, {characterData: true, subtree: true});
            }

            if (node.nodeType === 1 && (chatInput = node.querySelector('textarea#input-chat')) !== null) {
                chatInput.addEventListener('keydown', (event) => {
                    if (event.key == 'Tab' && tabCompletion.attempt(event.currentTarget)) {
                        event.preventDefault();
                    }
                });
            }
            
            if (node.nodeType === 1 && (username = node.querySelector('a.name')) !== null) {
                if (!username.text.trim().startsWith('{')) {
                    tabCompletion.addUsername(username.text.trim());
                }
            }

            if (node.nodeType === 1 && (messageContent = node.querySelector('div.message-content-main')) !== null) {
                if (tabCompletion.ownUsernameRegExp !== null) {
                    const updated = messageContent.innerHTML.replace(tabCompletion.ownUsernameRegExp,
                        '<span style="font-weight: bold">$&</span>');

                    if (messageContent.innerHTML !== updated) {
                        messageContent.innerHTML = updated;
                        messageContent.parentNode.classList.add('highlighted');
                    }
                }
            }
        }
    }
})).observe(document, {childList: true, subtree: true});