TypeScript icon, indicating that this package has built-in type declarations

19.0.0 • Public • Published


@ima/cli webpack HMR and @ima/error-overlay companion client.

Apart from connecting to webpack-hot-middleware SSE on the dev server, it initializes window.__IMA_HMR object that serves as an API for proper handling of HMR on IMA.js applications and controling @ima/error-overlay. It also manages rendering of the HMR Indicator icon in the lower right corner of the screen.


The companion script is injected at the top of the entry points in the webpack configuration, which then initializes the event emitter, event source and indicator singletons on the window.__IMA_HMR upon application load (see interface description below).

This client code directly replaces the ones used in webpack-hot-middleware, however we are still using webpack-hot-middleware on the server-side to send compilation events using SSE EventSource.

In combination with webpack-dev-middleware (which sends hot* update files to the application) and events from webpack-hot-middleware SSE, the client is using the webpack's Hot Module API to apply new hot updates to the client's source code. Additionally, it proxies compilation errors to error overlay and manages the HMR indicator icon in the lower right corner.


Use this package as an entry point in your webpack configuration (ideally at the topmost position on every additional entry point separately!). You can also customize some additional configuration that is passed to the client during initialization. Only name is required, other options have their defaults.

// webpack.config.js
module.exports = {
  // ...
  entry: {
    client: [
      `@ima/hmr-client?${new URLSearchParams({
        name: 'client', // required
        noInfo: 'false',
        reload: 'true',
        timeout: '3000',
        reactRefresh: 'true',
        port: '3101',
        hostname: 'localhost',
        publicUrl: 'http://localhost:3101',
  // ...

These options should match the actual dev server configuration since the HMR client uses them to connect to the webpack-hot-middleware event source.

window.__IMA_HMR interface

import { Emitter } from '@esmj/emitter';

interface Window {
  __IMA_HMR: {
    emitter?: Emitter;
    eventSource?: EventSourceWrapper;
    indicator?: IndicatorWrapper;



@esmj/emitter used to emit messages across application, error-overlay and hmr-client. It has 2 public methods:

  • on(eventName: EventName, listener: Listener): void; - use to listen on events ('error' | 'clear' | 'close' | 'destroy')
  • emit(eventName: EventName, data?: ListenerData): void; - use to emit events, only 'error' event is expected to pass any data in following form { error: {} }.
    • error - Send error object to ErrorOverlay.
    • clear - Clear all currently displayed errors in ErrorOverlay.
    • close - Close ErrorOverlay externally.
    • destroy - Destroy IMA.js application (destroys current instance before new one is created during HMR).



Singleton wrapper around webpack-hot-middleware SSE EventSource. You can use addListener public method to add custom listeners to the SSE events.

  • addListener(name: string, listener: EventSourceListener) - where name corresponds to the name value passed in webpack.config query params. This allows support for MultiComplier webpack instances.



Use to manage HMR State Indicator icon, has 2 public methods:

  • create(state: 'invalid' | 'loading' = 'loading'): void - Adds icon to the DOM in on of the selected visual states.
  • destroy(): void - Removes Icon from the DOM.

This package is part of the IMA.js application stack, see imajs.io for more info about the whole project.

Package Sidebar


npm i @ima/hmr-client

Weekly Downloads






Unpacked Size

44.4 kB

Total Files


Last publish


  • corvidism
  • mjancarik
  • filipoliko
  • matej.marcisovsky
  • jsimck
  • hartja
  • zdenek.lastuvka
  • jan.kucera
  • ondrej.sliva