main.js

// Modules to control application life and create native browser window
const {app, BrowserWindow} = require('electron');
const contextMenu = require('electron-context-menu');

contextMenu({
    append: (params) => [{
        label: 'Rainbow',
        // Only show it when right-clicking images
        visible: params.mediaType === 'image'
    }],
    showCopyImageAddress: true,
});

// Keep a global reference of the window object, if you don't, the window will
// be closed automatically when the JavaScript object is garbage collected.
let mainWindow;

function createWindow () {
    // Create the browser window.
    mainWindow = new BrowserWindow({
        width: 800,
        height: 600,
        webPreferences: {
            nodeIntegration: true
        }
    });

    // Load the index.html of the app.
    mainWindow.loadFile('index.html');

    // Emitted when the window is closed.
    mainWindow.on('closed', function () {
        // Dereference the window object
        mainWindow = null;
    });
}

// This method will be called when Electron has finished
// initialization and is ready to create browser windows.
// Some APIs can only be used after this event occurs.
app.on('ready', createWindow);

// Quit when all windows are closed.
app.on('window-all-closed', function () {
    // On macOS it is common for applications and their menu bar
    // to stay active until the user quits explicitly with Cmd + Q
    if (process.platform !== 'darwin') app.quit();
});

app.on('activate', function () {
    // On macOS it's common to re-create a window in the app when the
    // dock icon is clicked and there are no other windows open.
    if (mainWindow === null) createWindow();
});