How can I polyfill Promise with webpack?

For people using babel in combination with webpack: you can use babel-polyfill

Just do npm install --save "babel-polyfill" and then add it as an entry point in your webpack.config.js:

module.exports = {
   entry: ['babel-polyfill', './app/js']
};

Or, instead of using the entire babel-polyfill you can install core-js and reference only the module you need.

module.exports = {
   entry: ['core-js/stable/promise', './app/js']
};