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HTML Rewriter

WASM-based implementation of Cloudflare’s HTML Rewriter for use in Deno, browsers, etc.

It uses lol-html under the hood, the same implementation used by Cloudflare Workers. It is based on Miniflare’s WASM build.


This package includes 2 versions of HTML Rewriter.

index.ts loads the WASM that is co-located with this module via fetch and (streaming-) instantiates the module that way. In Deno, this works via file system (if you’ve downloaded the module) and web (when loading from or even However, if you are using this version with other tooling, depending on the bundler and configuration the WASM source may or may not be included…

base64.ts has the required WASM inlined as compressed base64. The total size is 447K (345K gzipped). This ensures that HTML Rewriter is working properly when bundled, offline, etc. The “hackyness” of ~400K of inlined WASM and relying on DecompressionStream is significant (without compression, the file size would be 1.2MB), but its simplicity makes it easier to get it to work with various bundlers (including Deno’s own, as of this writing).

Use in Browser

For use in the browser it’s best to install the “node-ified” package from npm and use it with a bundler.

npm install @worker-tools/html-rewriter

Which version of HTML Rewriter to pick depends on which bundler you are using:

For Webpack 4, it’s best to use the non-ESM base64 version via its full path: @worker-tools/html-rewriter/script/base64.

Webpack 5 treats the regular version correctly by default, which can be imported as @worker-tools/html-rewriter.

For esbuild it’s best to use the base64-version via @worker-tools/html-rewriter/base64.

You can explore the full contents of the npm package here.


import { 
} from ''

new HTMLRewriter()
  .on("p", {
    element(element) { 
      element.tagName = "h1" 
  .transform(new Response('<p class="red">test</p>'))
  .text().then(x => console.log(x))

For more on how to use HTMLRewriter, see the Cloudflare Workers Docs.


Make sure you’ve initialized all git submodules. It is 2 levels deep.

git submodule update --init --recursive

Make sure you have rustup installed. Then run

make dist

This will build a custom version of wasm-pack first, then use it to compile lol-html to WASM. Please see the submodules for details on why this is necessary.