Rocket.Chat/app/issuelinks/client/client.js

export const createIssueLinksMessageRenderer = ({ template }) => (message) => {
	if (!message.html?.trim()) {
		return message;
	}

	message.html = message.html.replace(/(?:^|\s|\n)(#[0-9]+)\b/g, (match, issueNumber) => {
		const url = template.replace('%s', issueNumber.substring(1));
		return match.replace(issueNumber, `<a href="${ url }" target="_blank">${ issueNumber }</a>`);
	});

	return message;
};