index.js

/**
 * Waits for the condition function to return a truthy value.
 * @param  {Function} Promise An ES6-compatible Promise implementation.
 * @param  {Function} condition The function that will be called to check the condition.
 * @param {Number} [interval=50] The interval in which to check the condition.
 * @return {Promise.<*>} Resolves what the either condition or value function returned.
 */
function waitFor(Promise, condition, interval) {
	interval = interval || 50;
	return new Promise(function (resolve, reject) {
		var int = setInterval(function () {
			try {
				var isDone = condition();
				if (isDone) {
					resolve(isDone);
					clearInterval(int);
				}
			} catch (err) {
				clearInterval(int);
				reject(err);
			}
		}, interval);
	});
}

/**
 * Binds waitFor to the specified promise implementation.
 * @param  {Function} Promise The promise constructor.
 * @return {Function} Returns the bound waitFor function.
 */
function use(Promise) {
	return waitFor.bind(null, Promise);
}

module.exports = use(Promise);
module.exports.use = use;