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Execute JavaScript in remote Electron processes, but more betterer

electron-remote: an asynchronous 'remote', and more

electron-remote provides an alternative to Electron's remote module based around Promises instead of synchronous execution. It also provides an automatic way to use BrowserWindows as "background processes" that auto-scales based on usage, similar to Grand Central Dispatch or the .NET TPL Taskpool.

The Quickest of Quick Starts

Calling code in other windows
import { createProxyForRemote } from 'electron-remote';
// myWindowJs is now a proxy object for myWindow's `window` global object 
const myWindowJs = createProxyForRemote(myWindow);
// Functions suffixed with _get will read a value 
userAgent = await myWindowJs.navigator.userAgent_get()
Renderer Taskpool
import { requireTaskPool } from 'electron-remote';
const myCoolModule = requireTaskPool(require.resolve('./my-cool-module'));
// This method will run synchronously, but in a background BrowserWindow process 
// so that your app will not block 
let result = await myCoolModule.calculateDigitsOfPi(100000);

But I like Remote!

Remote is super convenient! But it also has some downsides - its main downside is that its action is synchronous. This means that both the main and window processes will wait for a method to finish running. Even for quick methods, calling it too often can introduce scroll jank and generally cause performance problems.

electron-remote is a version of remote that, while less ergonomic, guarantees that it won't block the calling thread.

Using createProxyForRemote

createProxyForRemote is a replacement for places where you would use Electron's executeJavaScript method on BrowserWindow or WebView instances - however, it works a little differently. Using a new feature in ES2015 called proxy objects, we create an object which represents the window object on a remote context, and all method calls get sent as messages to that remote instead of being run immediately, which feels very similar to the remote Electron module.

This provides a number of very important advantages:

  • createProxyForRemote uses asynchronous IPC instead of blocking
  • Parameters are serialized directly, so you don't have to try to build strings that can be evald, which is a dangerous endeavor at best.
  • Calling methods on objects is far more convenient than trying to poke at things via a remote eval.

How do I get properties if everything is a Promise tho???

Astute observers will note, that getting the value of a property is always a synchronous operation - to facilitate that, any method with _get() appended to it will let you fetch the value for the property.

import { createProxyForRemote } from 'electron-remote';
// myWindowJs is now a proxy object for myWindow's `window` global object 
const myWindowJs = createProxyForRemote(myWindow);
// Functions suffixed with _get will read a value 
  .then((agent) => console.log(`The user agent is ${agent}`));

But do this first!

Before you use createProxyForRemote, you must call initializeEvalHandler() in the target window on startup. This sets up the listeners that electron-remote will use.

Bringing it all together

// In my window's main.js 
window.addNumbers = (a,b) => a + b;
// In my main process 
let myWindowProxy = createProxyForRemote(myWindow);
myWindowProxy.addNumbers(5, 5)
  .then((x) => console.log(x));
>>> 10

Here Be Dragons

electron-remote has a number of significant caveats versus the remote module that you should definitely be aware of:

  • Remote values must be Serializable

Objects that you return to the calling process must be serializable (i.e. you can call JSON.stringify on it and get a valid thing)- this means that creating Classes won't work, nor will return objects like BrowserWindows or other Electron objects. For example:

let myWindowProxy = createProxyForRemote(myWindow);
// XXX: BAD - HTML elements aren't serializable 
let obj = myWindowProxy.document.createElement('h1');
  • Remote event listeners aren't supported

Anything that involves an event handler isn't going to work:

// XXX: BAD - You can't add event handlers 
myWindowProxy.document.addEventListener('onBlur', (e) => console.log("Blur!"));

The Renderer Taskpool

Renderer Taskpools provide an automatic way to use BrowserWindows as "background processes" that auto-scales based on usage, similar to Grand Central Dispatch or the .NET TPL Taskpool. This works by allowing you to provide a Module that you'd like to load in the remote processes, which will be loaded and unloaded on the fly according to demand.

Let's look at the example again:

import { requireTaskPool } from 'electron-remote';
const myCoolModule = requireTaskPool(require.resolve('./my-cool-module'));
// This method will run synchronously, but in a background BrowserWindow process 
// so that your app will not block 
let result = await myCoolModule.calculateDigitsOfPi(100000);

By default, requireTaskPool will create up to four background processes to concurrently run JS code on. As these processes become busy, requests will be queued to different processes and wait in line implicitly.

More Dragons

Since requireTaskPool will create and destroy processes as needed, this means that global variables or other state will be destroyed as well. You can't rely on setting a global variable and having it persist for a period of time longer than one method call.

The remote-ajax module

One module that is super useful to have from the main process is a way to make network requests using Chromium's networking stack, which correctly does things such as respecting the system proxy settings. To this end, electron-remote comes with a convenient wrapper around Rx-DOM's AJAX methods called remote-ajax.

import { requireTaskPool } from 'electron-remote';
const remoteAjax = requireTaskPool(require.resolve('electron-remote/remote-ajax'));
// Result is the object that XmlHttpRequest gives you 
let result = await remoteAjax.get('');
>>> ''

See the documentation for Rx-DOM for how these methods work.

Another method that is included is downloadFileOrUrl, which lets you download a file to a target:

 * Downloads a path as either a file path or a HTTP URL to a specific place
 * @param  {string} pathOrUrl   Either an HTTP URL or a file path.
 * @return {string}             The contents as a UTF-8 decoded string.
function downloadFileOrUrl(pathOrUrl, target)