Marked Documentation

The parse function

import { marked } from 'marked';
marked.parse(markdownString [,options] [,callback])

Alternative using reference

// Create reference instance
import { marked } from 'marked';

// Set options
// `highlight` example uses https://highlightjs.org
marked.setOptions({
  renderer: new marked.Renderer(),
  highlight: function(code, lang) {
    const hljs = require('highlight.js');
    const language = hljs.getLanguage(lang) ? lang : 'plaintext';
    return hljs.highlight(code, { language }).value;
  },
  langPrefix: 'hljs language-', // highlight.js css expects a top-level 'hljs' class.
  pedantic: false,
  gfm: true,
  breaks: false,
  sanitize: false,
  smartLists: true,
  smartypants: false,
  xhtml: false
});

// Compile
console.log(marked.parse(markdownString));

Options

Inline Markdown

You can parse inline markdown by running markdown through marked.parseInline.

const blockHtml = marked.parse('**strong** _em_');
console.log(blockHtml); // '<p><strong>strong</strong> <em>em</em></p>'

const inlineHtml = marked.parseInline('**strong** _em_');
console.log(inlineHtml); // '<strong>strong</strong> <em>em</em>'

Asynchronous highlighting

Unlike highlight.js the pygmentize.js library uses asynchronous highlighting. This example demonstrates that marked is agnostic when it comes to the highlighter you use.

marked.setOptions({
  highlight: function(code, lang, callback) {
    require('pygmentize-bundled') ({ lang: lang, format: 'html' }, code, function (err, result) {
      callback(err, result.toString());
    });
  }
});

marked.parse(markdownString, (err, html) => {
  console.log(html);
});

In both examples, code is a string representing the section of code to pass to the highlighter. In this example, lang is a string informing the highlighter what programming language to use for the code and callback is the function the asynchronous highlighter will call once complete.

Workers

To prevent ReDoS attacks you can run marked on a worker and terminate it when parsing takes longer than usual.

Marked can be run in a worker thread on a node server, or a web worker in a browser.

Node Worker Thread

// markedWorker.js

import { marked } from 'marked';
import { parentPort } from 'worker_threads';

parentPort.on('message', (markdownString) => {
  parentPort.postMessage(marked.parse(markdownString));
});

// index.js

import { Worker } from 'worker_threads';
const markedWorker = new Worker('./markedWorker.js');

const markedTimeout = setTimeout(() => {
  markedWorker.terminate();
  throw new Error('Marked took too long!');
}, timeoutLimit);

markedWorker.on('message', (html) => {
  clearTimeout(markedTimeout);
  console.log(html);
  markedWorker.terminate();
});

markedWorker.postMessage(markdownString);

Web Worker

NOTE: Web Workers send the payload from postMessage in an object with the payload in a .data property

// markedWorker.js

importScripts('path/to/marked.min.js');

onmessage = (e) => {
  const markdownString = e.data
  postMessage(marked.parse(markdownString));
};

// script.js

const markedWorker = new Worker('./markedWorker.js');

const markedTimeout = setTimeout(() => {
  markedWorker.terminate();
  throw new Error('Marked took too long!');
}, timeoutLimit);

markedWorker.onmessage = (e) => {
  clearTimeout(markedTimeout);
  const html = e.data;
  console.log(html);
  markedWorker.terminate();
};

markedWorker.postMessage(markdownString);