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Browser module loading tests

This sample takes moment.js and three.js, and prepares them for loading in the browser with ECMAScript modules.


Cloning this repository

Standard stuff :) Hit the "Clone or download" button in the project's GitHub landing page and go from there.

Installing dependencies

NPM packages need to be installed on the root and both src/ subdirectories.

npm i

Gulp needs to be available globally. You can install it by doing:

npm i -g gulp

Building and developing

gulp build

Running the HTTP server

First add cert.pem and key.pem files for TLS. If you don't have these, you can use simplehttp2server to generate them for you. Place them at the root of the clone.


go run server/server.go

Or, if you don't have go command, you can use the built in HTTP server instead:

gulp serve

HTTP server command line options:

  • --http1: serve over HTTP/1.1 instead of HTTP/2
  • --push: use HTTP/2 push when serving
  • --preload: inject <link rel="preload"> tags for JS dependencies when serving

E.g., to serve over HTTP/1.1 with preload enabled:

go run server/server.go --http1 --preload

Bundled / unbundled tests

The bundled / unbundled test cases are served at the following URLs:

These tests load the files only once, so the results may be noisy. At the toplevel test page https://localhost:44333/ you can run the unbundled test cases repeatedly (25 times) and see the median time.

Synthesized module tree tests

In addition to the real-world library test cases, this HTTP server provides a benchmark for artificial module tree shapes. This is served at https://localhost:44333/synthesized/ and it accepts the following query parameters:

  • depth (default: 5): height of the module dependency tree
  • branch (default: 2): number of child modules non-leaf modules have
  • delay=n (optional): sleep n milliseconds in response handler
  • cacheable (optional): make JavaScript resources cacheable

E.g., this loads a module whose dependency tree is a perfect binary tree of depth 10 (2047 modules in total): https://localhost:44333/synthesized/?depth=10&branch=2

Note: Currently, --push and --preload options are not supported in synthesized tests.

[Experimental] WebBundle tests

Web Bundle is a file format for encapsulating one or more HTTP resources. It allows distributing a large number of module scripts as a single HTTP resource.

You need WebBundle Go tools to generate Web Bundles, which can be installed by this command:

go get -u

Then, this command will generate Web Bundles for the moment.js / three.js tests:


As of April 2020, Web Bundles support is implemented only in Chromium-based browsers, behind an experimental feature flag. To enable Web Bundles in Chrome, turn on chrome://flags/#web-bundles flag.

After enabling the flag, drag and drop samples-module-loading-comparison.wbn into Chrome to open it. An index page will be displayed from which you can choose a benchmark to run. also generates dist/moment/momentjs.wbn and dist/three/threejs.wbn. They only bundle the module scripts for each test. These can be used with dist/{moment,three}/webbundle.html to test Subresource loading with Web Bundles. (Note: this is a proposal in very early stage; experimental implementation is not landed in any browsers as of April 2020.)


Some tests for comparing performance between bundling and unbundling JS








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