Running Electron directly (electron app.js) vs. running from package.json script (npm run electron)

I have a simple Electron tray app with the following source:

const { app, Tray, Notification, Menu, nativeImage } = require('electron');
const path = require('path');

const iconPath = path.join(__dirname, 'assets/icons/iconTemplate.png');

let tray = null;

app.whenReady().then(() => {
    try {
        console.log(iconPath);
        tray = new Tray(nativeImage.createFromPath(iconPath));
        tray.setToolTip('Electron app');
    } catch (e) {
        console.log(e);
    }
})

Here's the package.json:

{
  "name": "Electron app",
  "version": "0.0.1",
  "description": "",
  "main": "app.js",
  "scripts": {
    "electron": "electron app.js",
    "test": "echo \"Error: no test specified\" && exit 1",
    "package-linux": "electron-packager . --overwrite --icon=assets/icons/256x256.png --out=release-builds",
    "deb64": "electron-installer-debian --config config/build-config.json"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "dependencies": {
    ...
  },
  "devDependencies": {
    ...
  }
}

When I run the app with electron app.js, nothing happens. But when I run npm run electron (which runs the script from package.json) the app works. What's the difference?