#12 You know nothing (medium)

promisify-example.js

function withCallback (message, callback) {
	callback(message);
}

function promisify (functionToCall) {
	return function promisifiedFunction () {
		// Before new Promise otherwise arguments value change
		var callArguments = Array.from(arguments);

		return new Promise (function (resolve, reject) {
			// Defined here for resolve to be defined
			var callback = function (result) {
				resolve(result); 
			};

			var argumentsForFunction = callArguments.concat(callback);
			functionToCall.apply(null, argumentsForFunction);
		});
	}
}

// Callback
withCallback('Callback', data => console.log(data));

// Promise
var withPromise = promisify(withCallback);
withPromise('One promise')
    .then(data => console.log(data));