How to pass parameters from main process to render processes in Electron

Question

I have an Electron app that can open different windows.

On app launch the app open a set of window(s) (that load the same HTML and JS files) but with params to change ea

Answer 1

For example:

Process script

In your main script write:

global.varsForWindow = {
    platform: process.platform
};

Window script

Where you need it in a window script:

var varsFromMainScript = require('electron').remote.getGlobal('varsForWindow');
console.log(varsFromMainScript.platform);

Answer 2

A few methods:

loadURL Query String

The query string method others have posted seems to work fine. It might even be the easiest.

additionalArguments

Electron's documentation says additionalArguments is:

Useful for passing small bits of data down to renderer process preload scripts.

Main

const win = new BrowserWindow({
  width: 800,
  height: 600,
  backgroundColor: '#000000'
  webPreferences: {
    additionalArguments: ["myvarvalue", "secondvarvalue", "--another=something"]
  }
});

Renderer

window.process.argv is going to look something like:

["--num-raster-threads=2",
"--enable-gpu-memory-buffer-compositor-resources",
"--enable-gpu-async-worker-context",
...
"--renderer-client-id=4",
"myvarvalue",
"secondvarvalue",
"--another=something"]

It will append an array of strings. You could do something window.process.argv.slice(-3) to grab the last items in the array.

---

IPC Main / Render

Like you said, it seems complicated for what you are trying to do, but maybe this helps:

Main

const { ipcMain } = require('electron');

var mainProcessVars = {
  somevar: "name",
  anothervar: 33
}

ipcMain.on('variable-request', function (event, arg) {
  event.sender.send('variable-reply', [mainProcessVars[arg[0]], mainProcessVars[arg[1]]]);
});

Renderer

const { ipcRenderer } = electron;

electron.ipcRenderer.send('variable-request', ['somevar', 'anothervar']);

ipcRenderer.on('variable-reply', function (event, args) {
  console.log(args[0]); // "name"
  console.log(args[1]); // 33
});

This way allows you to send data besides strings.

Answer 3

Using query string along with win.loadFile(),

// main process or renderer process 1
data = {"age": 12, "healthy": true}

let win = new BrowserWindow({
        webPreferences: {
          nodeIntegration: true
        }
      });

win.loadFile("public/print.html", {query: {"data": JSON.stringify(data)}});

// renderer process 2
const querystring = require('querystring');
let query = querystring.parse(global.location.search);
let data = JSON.parse(query['?data'])

Answer 4

You can share data between main and renderer processor using global variable:

Main processor:

global.id = 1;

Renderer processor:

let id = remote.getGlobal('id');

Answer 5

We can inject Javascript code execution (on window did-finish-load event) and trigger react re-rendering with correct redux state portion. But it requires additional lifecycle step in rendered process.

Using hash or query in "local filepath" sounds a little bit weird but in my case it take sense since the hash describe the redux store branch to take in consideration in this window (file://which-code-to-load#which-content).

So even if i'm not totally at ease with this approach right now I'll take the second option.

It's a shame that the API doesn't provide any way to declare global vars from main process on window opening. I'll post a feature request.

Answer 6

According atom source code the query string method is a reliable way to do that very simply, especially when we only need to pass a unique string param:

// main process
win1.loadURL(`file://${__dirname}/app/app.html?id=${id}`);

// rendered process
console.log(global.location.search);

https://github.com/electron/electron/issues/6504