electron-prevent-multiple-instances.js

var preventMultipleInstances = function(window) {
    var socket = (process.platform === 'win32') ? '\\\\.\\pipe\\myapp-sock' : path.join(os.tmpdir(), 'myapp.sock');
    net.connect({path: socket}, function () {
        var errorMessage = 'Another instance of ' + pjson.productName + ' is already running. Only one instance of the app can be open at a time.'
        dialog.showMessageBox(window, {'type': 'error', message: errorMessage, buttons: ['OK']}, function() {
            window.destroy()
        })
    }).on('error', function (err) {
        if (process.platform !== 'win32') {
            // try to unlink older socket if it exists, if it doesn't,
            // ignore ENOENT errors
            try {
                fs.unlinkSync(socket);
            } catch (e) {
                if (e.code !== 'ENOENT') {
                    throw e;
                }
            }
        }
        net.createServer(function (connection) {}).listen(socket);;
    });
}