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Using deno-dom with Deno

deno-dom is an implementation of DOM and HTML

parser in Deno. It is implemented in Rust (via Wasm) and TypeScript. There is also a “native” implementation, leveraging the FFI interface.

deno-dom aims for specification compliance, like jsdom and unlike LinkeDOM. Currently, deno-dom is slower than LinkeDOM for things like parsing data structures, but faster at some manipulation operations. Both deno-dom and LinkeDOM are significantly faster than jsdom.

As of deno_dom v0.1.22-alpha supports running on Deno Deploy. So if you want strict standards alignment, consider using deno-dom over LinkeDOM.

Basic example

This example will take a test string and parse it as HTML and generate a DOM structure based on it. It will then query that DOM structure, picking out the first heading it encounters and print out the text content of that heading:

import { DOMParser } from "https://deno.land/x/deno_dom/deno-dom-wasm.ts";
import { assert } from "https://deno.land/std@0.185.0/testing/asserts.ts";

const document = new DOMParser().parseFromString(
  `<!DOCTYPE html>
  <html lang="en">
    <head>
      <title>Hello from Deno</title>
    </head>
    <body>
      <h1>Hello from Deno</h1>
      <form>
        <input name="user">
        <button>
          Submit
        </button>
      </form>
    </body>
  </html>`,
  "text/html",
);

assert(document);
const h1 = document.querySelector("h1");
assert(h1);

console.log(h1.textContent);

Note: the example uses an unpinned version from deno_land/x, which you likely don’t want to do, because the version can change and cause unexpected outcomes. You should use the latest version of available of deno-dom.

Faster startup

Just importing the deno-dom-wasm.ts file bootstraps the Wasm code via top level await. The problem is that top level await blocks the module loading process. Especially with big Wasm projects, it is a lot more performant to initialize the Wasm after module loading is complete.

deno-dom has the solution for that, they provide an alternative version of the library that does not automatically init the Wasm, and requires you to do it in the code:

import {
  DOMParser,
  initParser,
} from "https://deno.land/x/deno_dom/deno-dom-wasm-noinit.ts";

(async () => {
  // initialize when you need it, but not at the top level
  await initParser();

  const doc = new DOMParser().parseFromString(
    `<h1>Lorem ipsum dolor...</h1>`,
    "text/html",
  );
})();

In addition, using the deno-dom-native.ts (which requires the --allow-ffi flag) will bypass the Wasm startup penalty as well as will not require the init() startup time. This would only work with the Deno CLI and not Deploy.

Using LinkeDOM
Using jsdom