VSCode Extension

For an easy fully local workflow try the JSPM Generator VSCode Extension, which is supported as a Web Extension.

This provides a workflow for writing native HTML imports directly, then post-processing the HTML file to insert the generated import map and polyfill.

With the extension installed, create a new VSCode project, with an app.html file:

<!doctype html>
<script type="module" src="./lib/app.js"></script>

Then create a new JS file lib/app.js:

import lit from 'lit';

With the editor focus on app.html open the VSCode Command Palette (Ctrl + Shift + P) and select the JSPM: Generate Import Map command

The first question will be whether to inject preloads and integrity for the generation process, in this case select No:

This preference can also be saved and changed any time from the VSCode JSPM Settings.

The final question is what environments to generate the import map for. The default generation is with the browser, development and module exports conditions, in this case we select a production instead of a development import map:

Press return again and the generator will run the complete generation API from within VSCode, modifying the HTML to include the injected import map on completion.

The app.html file will then be updated by the extension with the ES Module Shims polyfill and import map tags:

<!doctype html>
<!-- Generated by @jspm/generator VSCode Extension - https://github.com/jspm/jspm-vscode -->
<script async src="https://ga.jspm.io/npm:es-module-shims@1.4.7/dist/es-module-shims.js" crossorigin="anonymous"></script>
<script type="importmap">
  "scopes": {
    "./": {
      "lit": "https://ga.jspm.io/npm:lit@2.2.0/index.js"
    "https://ga.jspm.io/": {
      "@lit/reactive-element": "https://ga.jspm.io/npm:@lit/reactive-element@1.3.0/reactive-element.js",
      "lit-element/lit-element.js": "https://ga.jspm.io/npm:lit-element@3.2.0/lit-element.js",
      "lit-html": "https://ga.jspm.io/npm:lit-html@2.2.0/lit-html.js"
<script type="module" src="./lib/app.js"></script>

Rewriting will carefully respect existing HTML and existing import mappings. The operation is also largely idempotent unless there are resolution differences.

Version ranges will be consulted from any local package.json file. The full Node.js resolver rules are supported so it's even possible to use own-name resolution and package imports resolution while respecting custom local import map mappings.

After processing, app.html should then be a fully executable HTML application. For production it is usually advisable to use the preload option which will inject integrity as well for static guarantees.

Vite Plugin

Vite is architected primarily to modern ES modules workflows, making JSPM and Vite a great combination.

With the JSPM Vite plugin, ddependencies are retrieved from JSPM while the project is bundled using Vite.

npm install vite-plugin-jspm --save-dev

vite and vite build can be used for dev server and production builds respectively. The plugin takes all the options that are supported with @jspm/generator.


import { defineConfig } from 'vite';
import jspmPlugin from 'vite-plugin-jspm';

export default defineConfig({
  plugins: [jspmPlugin()],

The plugin will automatically inject ES Module Shims to polyfill import maps.

An additional option that you can use is downloadDeps, to download and build all the dependencies from the JSPM CDN at build time.

When using the downloadDeps option, there are a number of factors that should be considered:

Node.js Loader

Status: Experimental

A loader for Node.js to HTTPs imports and import maps with JSPM.

See https://github.com/jspm/node-importmap-http-loader.

Import Map Rails

Import Map Rails provides Ruby on Rails dependency management with import maps and JSPM.