Rocket.Chat/app/ui/client/lib/codeMirror/codeMirrorComponent.js

import { Meteor } from 'meteor/meteor';
import { Session } from 'meteor/session';
import { Template } from 'meteor/templating';
import 'codemirror/lib/codemirror.css';
import CodeMirror from 'codemirror/lib/codemirror.js';

const CodeMirrors = {};

Template.CodeMirror.rendered = function() {
	const options = this.data.options || { lineNumbers: true };
	const textarea = this.find('textarea');
	const editor = CodeMirror.fromTextArea(textarea, options);

	CodeMirrors[this.data.id || 'code-mirror-textarea'] = editor;

	const self = this;
	editor.on('change', function(doc) {
		const val = doc.getValue();
		textarea.value = val;
		if (self.data.reactiveVar) {
			Session.set(self.data.reactiveVar, val);
		}
	});

	if (this.data.reactiveVar) {
		this.autorun(function() {
			const val = Session.get(self.data.reactiveVar) || '';
			if (val !== editor.getValue()) {
				editor.setValue(val);
			}
		});
	}

	Meteor.defer(function() {
		editor.refresh();
	});
};

Template.CodeMirror.destroyed = function() {
	delete CodeMirrors[this.data.id || 'code-mirror-textarea'];
	this.$(`#${ this.data.id || 'code-mirror-textarea' }`).next('.CodeMirror').remove();
};

Template.CodeMirror.helpers({
	editorId() {
		return this.id || 'code-mirror-textarea';
	},

	editorName() {
		return this.name || 'code-mirror-textarea';
	},
});