To test actual effect of JS timer to show they are not accurate

main.js

'use strict';
/**
 * Created by zyf on 17-4-19.
 */
let i;
let times = 10,
	delay = 100;
let startTime, lastTime, now, durations;

const workNum = 100000;
let workResult = [];
const init = (_times, _delay, _work, _endWork) => {
	i = 0;
	durations = [];
	workResult = [];
	lastTime = startTime = Date.now();
	
	_times > 0 && (times = _times);
	_delay > 0 && (delay = _delay);
	_work && (work = _work);
	_endWork && (endWork = _endWork)
};
let work = (timer) => {
	// waste time
	for (let i = 0; i < workNum; i++) {
		workResult.push(i)
	}
};
let endWork = () => {
	for (let i = 0; i < workResult.length; i++) {
		if (i == 0) {
			continue
		}
		let num = workResult[i];
		if (num === 0) {
			num = workNum;
		}
		if (num - 1 != workResult[i - 1]) {
			return console.error('bad workResult')
		}
	}
	console.log('good workResult')
};

const handle = (which, timer, next) => {
	now = Date.now();
	durations.push(now - lastTime);
	lastTime = now;
	i++;
	if (i === times) {
		which === 'interval' && clearInterval(timer);
		which === 'timeout' && clearTimeout(timer);
		console.log(which);
		const pastTime = now - startTime;
		console.log('workTimes', times, 'real times', durations.length);
		const expectTime = times * delay;
		console.log(
			'expect time', expectTime,
			'real pastTime', pastTime,
			'over percent', ((pastTime - expectTime) / expectTime * 100).toFixed(3) + ' %'
		);
		console.log(
			'expect duration', delay,
			'real average duration', (pastTime / times).toFixed(3)
		);
		endWork();
		next && setTimeout(next, 0);
	}
};

const timeoutDo = (next) => {
	const _do = (timer) => {
		work(timer);
		timer = setTimeout(() => {
			_do(timer)
		}, delay);
		handle('timeout', timer, next);
	};
	let timer = setTimeout(() => {
		_do(timer)
	}, delay);
	return timer
};
const intervalDo = (next) => {
	const timer = setInterval(() => {
		work(timer);
		handle('interval', timer, next);
	}, delay);
	return timer
};

module.exports = {
	init: init,
	timeoutDo: timeoutDo,
	intervalDo: intervalDo
};

// init(100, 100)
// timeoutDo()