electron/docs/api/remote.md

remote

The remote module provides a simple way to do inter-process communication between the renderer process and the main process.

In Electron, only GUI-unrelated modules are available in the renderer process. Without the remote module, users who wanted to call a main process API in the renderer process would have to explicitly send inter-process messages to the main process. With the remote module, users can invoke methods of main process object without explicitly sending inter-process messages, similar to Java's RMI.

An example of creating a browser window in renderer process:

var remote = require('remote');
var BrowserWindow = remote.require('browser-window');
var win = new BrowserWindow({ width: 800, height: 600 });
win.loadUrl('https://github.com');

Note: for the reverse (access renderer process from main process), you can use webContents.executeJavascript.

Remote objects

Each object (including functions) returned by the remote module represents an object in the main process (we call it a remote object or remote function). When you invoke methods of a remote object, call a remote function, or create a new object with the remote constructor (function), you are actually sending synchronous inter-process messages.

In the example above, both BrowserWindow and win were remote objects and new BrowserWindow didn't create a BrowserWindow object in the renderer process. Instead, it created a BrowserWindow object in the main process and returned the corresponding remote object in the renderer process, namely the win object.

Lifetime of remote objects

Electron makes sure that as long as the remote object in the renderer process lives (in other words, has not been garbage collected), the corresponding object in the main process would never be released. When the remote object has been garbage collected, the corresponding object in the main process would be dereferenced.

If the remote object is leaked in renderer process (e.g. stored in a map but never freed), the corresponding object in the main process would also be leaked, so you should be very careful not to leak remote objects.

Primary value types like strings and numbers, however, are sent by copy.

Passing callbacks to the main process

Code in the main process can accept callbacks from the renderer - for instance the remote module - but you should be extremely careful when using this feature.

First, in order to avoid deadlocks, the callbacks passed to the main process are called asynchronously. You should not expect the main process to get the return value of the passed callbacks.

For instance you can't use a function from the renderer process in a Array.map called in the main process:

// main process mapNumbers.js
exports.withRendererCallback = function(mapper) {
  return [1,2,3].map(mapper);
}

exports.withLocalCallback = function() {
  return exports.mapNumbers(function(x) {
    return x + 1; 
  });
}

// renderer process
var mapNumbers = require("remote").require("mapNumbers");

var withRendererCb = mapNumbers.withRendererCallback(function(x) {
  return x + 1;
})

var withLocalCb = mapNumbers.withLocalCallback()

console.log(withRendererCb, withLocalCb) // [true, true, true], [2, 3, 4]

As you can see, the renderer callback's synchronous return value was not as expected, and didn't match the return value of an indentical callback that lives in the main process.

Second, the callbacks passed to the main process will persist until the main process garbage-collects them.

For example, the following code seems innocent at first glance. It installs a callback for the close event on a remote object:

var remote = require('remote');
remote.getCurrentWindow().on('close', function() {
  // blabla...
});

But remember the callback is referenced by the main process until you explicitly uninstall it! If you do not, each time you reload your window the callback will be installed again, leaking one callback each restart.

To make things worse, since the context of previously installed callbacks have been released, when the close event was emitted exceptions would be raised in the main process.

To avoid this problem, ensure you clean up any references to renderer callbacks passed to the main process. This involves cleaning up event handlers, or ensuring the main process is explicitly told to deference callbacks that came from a renderer process that is exiting.

remote.require(module)

• module String

Returns the object returned by require(module) in the main process.

remote.getCurrentWindow()

Returns the BrowserWindow object which this web page belongs to.

remote.getCurrentWebContents()

Returns the WebContents object of this web page.

remote.getGlobal(name)

• name String

Returns the global variable of name (e.g. global[name]) in the main process.

remote.process

Returns the process object in the main process. This is the same as remote.getGlobal('process'), but gets cached.