How to Convert Markdown to HTML in JavaScript

To convert Markdown to HTML in JavaScript, parse the Markdown with a library such as marked or markdown-it, then sanitize the resulting HTML with DOMPurify before inserting it into the page. Parsing alone is not enough: unsanitized HTML lets attackers inject scripts. Convert Markdown without writing code using our free Markdown to HTML converter.

The No-Code Method First: Convert in the Browser

Before writing any code, it is worth knowing that the conversion itself takes seconds without a library at all. Paste Markdown into a converter, copy the HTML out, and paste it where it belongs: a blog post, a documentation page, or an email template. That workflow fits one-off conversions, content migration, and anyone who does not run a JavaScript project. The reason developers still reach for a library is repetition: when Markdown arrives continuously, from user input, a content API, or a file watcher, a converter that runs in code converts it on demand, every time, without a manual paste step. The rest of this guide covers that programmatic path, and the trade-offs between the two main libraries. The important principle is the same in both cases: Markdown is a writing format, HTML is a display format, and the conversion should be a one-way, repeatable step that never edits the original Markdown. Our free Markdown to HTML converter runs entirely in your browser, so drafts never leave your device, and the Markdown to HTML online guide covers the no-code workflow in full.

Markdown to HTML JavaScript Library: marked in Three Steps

The marked library is the most widely used Markdown parser for JavaScript, and its basic use is three steps. First, install it in a Node project or load it in a browser page. Second, pass a Markdown string to its parse function, which returns an HTML string with headings, paragraphs, lists, links, and code blocks converted. Third, insert that HTML into the page only after sanitizing it, which the sanitization section below covers. A heading written with a hash becomes a heading element, bold text wrapped in double asterisks becomes a strong element, and a link written in bracket-and-parenthesis form becomes an anchor element, all exactly as the Markdown specification intends. The marked library is fast, actively maintained, and compatible with the CommonMark specification plus GitHub-flavored extensions such as tables, strikethrough, and task lists. Its default settings are deliberately simple, which makes it the right choice when you want standard Markdown conversion without configuring a plugin system. For the same conversion in Python, our Markdown to HTML in Python guide covers the equivalent libraries, and the Markdown to HTML converter shows what the output should look like for any input.

marked vs markdown-it: Which Parser to Pick

The two serious choices are marked and markdown-it, and the decision comes down to extensibility versus simplicity. Marked is the simpler, faster option: a single parser with sensible defaults, GitHub-flavored Markdown built in, and a small API surface that most projects learn in an afternoon. Markdown-it is the more extensible option: a plugin architecture that lets you add footnotes, definition lists, containers, emoji, and syntax highlighting as separate plugins, at the cost of a larger configuration surface. Performance differences between them are negligible for typical web content; both parse a blog post in milliseconds, and the bottleneck is almost always network or rendering, not parsing. The practical rule is to pick marked when you need standard Markdown conversion quickly, and markdown-it when you know you will need plugins, custom rendering rules, or fine-grained control over individual token types. A third option, showdown, still appears in older tutorials, but its maintenance has slowed and its output differs subtly from CommonMark in edge cases, so new projects should prefer the two maintained libraries. Whichever parser you pick, the sanitization step below is mandatory, not optional. Our Markdown table to HTML guide covers the table syntax both parsers handle, and the Markdown to HTML converter lets you compare parser output against a reference.

How to Sanitize HTML From Markdown in JavaScript

Sanitization is the step that separates a working converter from a security hole. Markdown allows raw HTML by design, so a Markdown document can contain an image tag with an event-handler attribute that runs code when the image fails to load, or a link with a javascript address that runs code when clicked, and a parser will faithfully convert both into HTML. If that HTML is inserted into a page without cleaning, the attacker's code runs in your visitors' browsers, stealing sessions and credentials. The standard fix is DOMPurify, a library that parses the HTML, removes dangerous elements and attributes, and returns clean HTML that keeps safe formatting such as headings, links, bold text, and lists. The workflow is to parse Markdown to HTML, pass the HTML through DOMPurify's sanitize function, and insert only the sanitized result into the page. Never insert parser output directly, never trust Markdown from untrusted users, and never allow raw HTML in user-submitted Markdown unless you have a sanitization step you have tested with hostile inputs. A useful test is to feed the converter a document containing a script element, an image with an event handler, and a javascript link, and confirm all three are stripped while ordinary formatting survives. Our Markdown to HTML converter handles the conversion step for trusted drafts, and the Markdown to HTML online guide explains the conversion itself without the code.

Rendering in the Browser vs Node, and Code Highlighting

Where the conversion runs changes the setup. In the browser, the parser and sanitizer load as scripts, convert Markdown on the page, and render the result immediately, which fits live previews, comment boxes, and documentation editors. In Node, the same libraries run at build time or on a server, converting Markdown files into HTML pages before deployment, which fits static sites, blogs, and documentation generators. The code is nearly identical in both environments, which is one reason JavaScript Markdown tooling is popular: the same parser serves the editor preview and the published page. Code highlighting is a separate step from parsing: parsers wrap code blocks in pre and code elements, and a highlighting library then colors the keywords inside, either at build time or in the browser. A common mistake is highlighting before sanitizing, which can reintroduce unsafe markup, so the safe order is parse, sanitize, then highlight. Dates inside Markdown frontmatter deserve the same care: a post's date field is often a timestamp, and our Unix timestamp in log files guide shows how to read one, while the Unix timestamp converter turns it into a readable date. For email, where JavaScript never runs, our Markdown in Python guide covers the server-side equivalent.

Mistakes to Avoid When Converting Markdown in JavaScript

Five mistakes cover nearly every bad Markdown conversion. First, skipping sanitization, which turns a converter into a cross-site scripting vulnerability, covered above. Second, using regular expressions to convert Markdown instead of a parser, which breaks on nested lists, code blocks containing Markdown-like text, and links with parentheses, all of which a real parser handles. Third, mixing parser output with hand-written HTML and assuming the result is safe, when only the sanitized combination is safe. Fourth, forgetting that different parsers render edge cases differently, so switching libraries mid-project changes published output and breaks tests that compare HTML strings exactly. Fifth, converting Markdown on every page render instead of caching the result, which wastes CPU on content that rarely changes; convert at save time or build time and cache the HTML. The discipline that avoids all five is simple: use a maintained parser, always sanitize, test with hostile input, pin the library version, and cache the output. Start with our free Markdown to HTML converter to see correct output for your own Markdown, then implement the same pipeline in code with marked or markdown-it plus DOMPurify.