Custom_main

This guide explains how to include and use a custom_main.js file in your Electron.NET application for advanced Electron/Node.js customization.

Why use custom_main.js?

• Register custom protocol handlers (e.g., myapp://) — protocols must be registered before the app is fully initialized
• Integrate Node.js modules (e.g., telemetry, OS APIs)
• Control startup logic (abort, environment checks)
• Modify Chromium / Electron.NET command line switches before they are evaluated
• Set up IPC messaging or preload scripts

Step-by-Step Process

1. Create the custom_main.js file

Place your custom logic in electron/custom_main.js:

module.exports.onStartup = function(host) {
    // Example: Register a global shortcut for opening dev tools
    const { app, globalShortcut, BrowserWindow } = require('electron');
    app.on('ready', () => {
        const ret = globalShortcut.register('Control+Shift+I', () => {
            BrowserWindow.getAllWindows().forEach(win => win.webContents.openDevTools());
            console.log('Ctrl+Shift+I is pressed: DevTools opened!');
        });
    });
    app.on('will-quit', () => {
        globalShortcut.unregisterAll();
    });
    return true;
};

2. Configure your .csproj to copy custom_main.js to output

Add this to your .csproj file:

<ItemGroup>
  <None Update="electron\custom_main.js">
    <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
    <TargetPath>.electron\custom_main.js</TargetPath>
  </None>
</ItemGroup>

3. Build and run your app

Use the standard build/run commands:

dotnet build
dotnet run

Electron.NET will automatically load and execute your custom_main.js before initializing the .NET backend.

Advanced Usage

Use environment variables to control features:

const env = process.env.ASPNETCORE_ENVIRONMENT || 'Production';
if (env === 'Development') { /* enable dev features */ }

Modifying Command Line Switches

onStartup is invoked before Electron.NET reads any of its own switches (manifest, unpackedelectron, unpackeddotnet, dotnetpacked, electronforcedport, electronurl), so the hook can append or override them:

module.exports.onStartup = function (host) {
    const { app } = require('electron');

    // Force a fixed socket bridge port
    app.commandLine.appendSwitch('electronforcedport', '8000');

    // Chromium switches, e.g. to disable the GPU sandbox
    app.commandLine.appendSwitch('disable-gpu-sandbox');

    return true;
};

Notes

• custom_main.js must use CommonJS syntax (module.exports.onStartup = ...).
• Place the file in your source directory and copy it to .electron using .csproj.
• Electron.NET will abort startup if onStartup returns false.
• onStartup runs before the Electron.NET command line switches are evaluated, so switches set there are picked up by the host.

Complete example is available here ElectronNetSampleApp