A userscript to add a Jira-Markdown converter to Jira text fields

jira-markdown-converter.user.js

// ==UserScript==
// @name         JIRA Markdown Converter
// @namespace    https://nickcoutsos.github.io/
// @version      0.1
// @description  Add context menu action to convert text in a field to/from Github Flavored Markdown
// @author       Nick Coutsos
// @match        https://*.atlassian.net/*
// @require      https://raw.githubusercontent.com/FokkeZB/J2M/master/src/J2M.js
// ==/UserScript==

var syntaxes = {
	jira: {converter: J2M.toM, label: 'Convert to Markdown'},
	markdown: {converter: J2M.toJ, label: 'Convert to JIRA'}
};

function watch(selector, interval, onChange) {
	if (typeof interval === 'function') {
		onChange = interval;
		interval = 200;
	}

	let timer = setInterval(function () {
		let element = document.querySelector(selector);
		if (element && !element.dataset.lastObserved) {
			element.setAttribute('data-last-observed', Date.now());
			onChange(element);
		}
	}, interval);
}

function addConverter(element) {
	var textarea = element.parentNode.parentNode.querySelector('textarea');
	var button = document.createElement('input');
	var isJira = true;

	button.type = 'image';
	button.src = 'https://cdn0.iconfinder.com/data/icons/octicons/1024/mark-github-128.png';
	button.height = '15';
	button.style.verticalAlign = 'text-top';

	button.setAttribute('state', 'g2j');
	element.appendChild(button);
	element.addEventListener('click', e => {
		e.preventDefault();
		var syntax = syntaxes[isJira ? 'jira' : 'markdown'];
		isJira = !isJira;

		button.alt = syntax.label;
		textarea.textContent = syntax.converter(textarea.textContent);
	});
}


(function() {
    'use strict';
	watch('.save-options .field-tools', addConverter);
})();