function-expectResult.js

Function.prototype.expectResult = async function expectResult(interval, timeout, expectValue) {
	if (interval <= 0)
		interval = 1000;
	var fn = this;
	var timeStart = Date.now();
	var tries = 0;
	function check() {
		var value, error, asExpected;
		try {
			value = fn();
		}
		catch (e) {
			error = e;
		}
		if (typeof expectValue === 'function')
			asExpected = expectValue(value);
		else if (typeof expectValue === 'boolean')
			asExpected = !!value == !!expectValue;
		else
			asExpected = value == expectValue;
		return {
			tries: ++tries,
			value: value,
			timeStart: timeStart,
			time: Date.now() - timeStart,
			asExpected: asExpected,
			error: error,
		};
	}
	return new Promise(function (resolve, reject) {
		function retry() {
			var res = check();
			if (timeout > 0 && !res.error && res.time > timeout) {
				res.error = new Error("Timeout");
			}
			if (res.asExpected) {
				resolve(res);
			}
			else if (res.error) {
				reject(res);
			}
			else {
				setTimeout(retry, interval);
			}
		}
		retry();
	});
};