No webpack, no parcel, no rollup, no npm, no friction. Just your code and your imagination.


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443Mar 8, 2020Jun 5, 2018Minified + gzip package size for @plnkr/runtime in KB



No webpack, no parcel, no rollup, no npm, no friction. Just your code and your imagination.

A browser-native tool for running modern javascript code, using npm dependencies without any tooling. Supports hot module reloading and css / less imports (more to come).

This is not for production, this is for experimentation without boilerplate overload or for use in niche developer tools like Plunker. Everything is loaded on the fly and, of course, this will impose certain performance limitations.


To get a hold of an instance of this module, all you need to do is:

Using the amazing jspm.io cdn:

    .then(esModule => esModule.default)
    .then(PlnkrRuntime => {
        // Let your imagination go wild

or using a popular cdn that fronts npm releases like unpkg:

<script src="https://unpkg.com/@plnkr/runtime"></script>
    const PlnkrRuntime = window.PlnkrRuntime;
    // Get weird


This example demonstrates an example where we define a custom react Component, pull this into another file and render it to a string using react-dom.

Note: No npm, no webpack, no parcel, no configuration, no friction. Just code and your imagination.

// We define a mock 'host' filesystem that represents the project we will run
const files = {
    'package.json': JSON.stringify({
        dependencies: {
            react: '16.x',
            'react-dom': '16.x',
    'index.js': `
        import React from 'react';
        import { renderToString } from 'react-dom/server';

        import Hello from './Hello';

        export const markup = renderToString(<Hello name="World"></Hello>);
    'Hello.js': `
        import React, { Component } from 'react';

        export default class Hello extends Component {
            render() {
                return <h1>Hello {this.props.name}</h1>;
// Next, we define a host that implements the RuntimeHost interface and resolves files from our mock filesystem
const host = {
    getCanonicalPath(path) {
        if (files[path]) return path;
        if (files[`${path}.js`]) return `${path}.js`;
        return Promise.reject(new Error(`File not found ${path}`));
    getFileContents(canonicalPath) {
        return files[canonicalPath];
// Now that we have a host, we can create a runtime instance
const runtime = new PlnkrRuntime.Runtime({ host });

// Now we run our example code that will pull in react and react-dom, will transpile our custom code and will
// then execute it in a context where bare modules are resolved for us.
const { markup } = await runtime.import('./index.js');


new PlnkrRuntime.Runtime({ host })

Creates a new Runtime instance where:

  • host is an object that implements the RuntimeHost interface.

runtime.import(key: string, parentKey?: string): Promise<ModuleInstance>

Import and run the the code from the canonical url determined by running runtime.resolve(key, parentKey).

Returns a Promise that will resolve to the module instance.

runtime.invalidate(...keys: string[]): Promise<void>

Invalidate the module instances, traversing up to all dependent modules and invalidating those as well where:

  • keys is one or more string arguments whose resolved paths will be invalidated.

Returns a Promise that will resolve when all requested modules and their dependents have been invalidated.

runtime.resolve(key: string, parentKey?: string): Promise<string>

Resolve absolute and relative paths and urls as well as bare module specifiers to their canonical url where:

  • key is a pointer to the file whose code should be imported and executed. This could point to different things:
    • ./relative/path in which case the Runtime will attempt to resolve this to a canonical url via the host.getCanonicalPath function. If that function is not present, the canonical url will be assumed to be the key.
    • npm-module in which case the Runtime will attempt to resolve the bare module version by attempting to load ./package.json and find its specifier in the dependencies or devDependencies mappings. If ./package.json is absent or no specifier could be resolved, the version will be assumed to be the latest tag.
  • parentKey is an optional url relative to which the key will be resolved. For example a key of ./foo and parentKey of ./folder/parent would resolve to ./folder/foo.

Returns a Promise that will resolve to the resolved, canonical url.


This is the interface that must be implemented by the host object passed to new PlnkrRuntime.Runtime({ host }).

RuntimeHost.getCanonicalPath?(key: string): string | PromiseLike<string>


Return the canonical path or a Promise that resolves for a given 'local' resource. A 'local' resource is one that is neither a bare module nor a url whose prefix doesn't match document.baseURI. This method should be implemented if you want to support importing relative files without their extensions and these can't be determined a priori.

RuntimeHost.getFileContents(key: string): string | PromiseLike<string>

Return the contents of the file (or a Promise thereof) whose canonical path is key.

Note: This interface will be called to resolve bare module versions with package.json as the key. If you want to control the versions of bare modules (npm modules), then a mock package.json can be returned here that defined the dependencies for the bare modules whose versions are important to you.

Thank you

This project was made possible by:

  • All the hard work by the collaborators of es-module-loader.
  • Guy Bedford and his jspm project and its 'magic' ES Module and System.register CDNs, dev.jspm.io and system-dev.jspm.io, respectively.

If you find any bugs or have a feature request, please open an issue on github!

The npm package download data comes from npm's download counts api and package details come from npms.io.