Fenced code blocks support language modifier

js/markdown.js

 		let openFenceLine = state.lines[p++];
 		var modifier;
 		[openFenceLine, modifier] = MDTagModifier.fromLine(openFenceLine);
-		if (openFenceLine.trim() != '```') return null;
+		const match = /^```\s*([a-z0-9]*)\s*$/.exec(openFenceLine);
+		if (match === null) return null;
+		const language = match[1].length > 0 ? match[1] : null;
 		var codeLines = [];
 		while (state.hasLines(1, p)) {
 			let line = state.lines[p++];
 			if (line.trim() == '```') {
 				state.p = p;
-				let block = new MDCodeBlockNode(codeLines.join("\n"));
+				let block = new MDCodeBlockNode(codeLines.join("\n"), language);
 				if (modifier) modifier.applyTo(block);
 				return block;
 			}
 	/** @type {string} */
 	text;
 
+	/** @type {string|null} */
+	language;
+
 	/**
 	 * @param {string} text
+	 * @param {string|null} language
 	 */
-	constructor(text) {
+	constructor(text, language=null) {
 		super([]);
 		this.text = text;
+		this.language = language;
 	}
 
 	toHTML(state) {
-		return `<pre${this._htmlAttributes()}><code>${MDUtils.escapeHTML(this.text)}</code></pre>\n`;
+		const languageModifier = (this.language !== null) ? ` class="language-${this.language}"` : '';
+		return `<pre${this._htmlAttributes()}><code${languageModifier}>${MDUtils.escapeHTML(this.text)}</code></pre>\n`;
 	}
 }
 

testjs.html

 					this.assertEqual(actual.replace(/ /g, '⎵'), expected.replace(/ /g, '⎵'));
 				}
 
+				test_codeBlock_fenced_language() {
+					let markdown = "Code\n\n```javascript\nfunction foo() {\n    return 'bar';\n}\n```\n\nend";
+					let expected = "<p>Code</p>\n\n<pre><code class=\"language-javascript\">function foo() {\n    return 'bar';\n}</code></pre>\n\n<p>end</p>";
+					let actual = this.parser.toHTML(markdown).trim(); // don't normalize whitespace
+					this.assertEqual(actual.replace(/ /g, '⎵'), expected.replace(/ /g, '⎵'));
+				}
+
 				test_horizontalRule() {
 					let markdown = "Before\n\n---\n\n- - -\n\n***\n\n* * * * * * *\n\nafter";
 					let expected = "<p>Before</p> <hr> <hr> <hr> <hr> <p>after</p>";