index.js

(function (factory) {
	if (typeof define === 'function' && define.amd) {
		define([], factory);
	} else if (typeof module === 'object' && module.exports) {
		module.exports = factory();
	} else {
		window.idleCallbackShim = factory();
	}
}(function(){
	'use strict';
	var scheduleStart, throttleDelay, lazytimer, lazyraf;
	var root = typeof window != 'undefined' ?
		window :
		typeof global != undefined ?
			global :
			this || {};
	var requestAnimationFrame = root.cancelRequestAnimationFrame && root.requestAnimationFrame || setTimeout;
	var cancelRequestAnimationFrame = root.cancelRequestAnimationFrame || clearTimeout;
	var tasks = [];
	var runAttempts = 0;
	var isRunning = false;
	var remainingTime = 7;
	var minThrottle = 35;
	var throttle = 125;
	var index = 0;
	var taskStart = 0;
	var tasklength = 0;
	var IdleDeadline = {
		get didTimeout(){
			return false;
		},
		timeRemaining: function(){
			var timeRemaining = remainingTime - (Date.now() - taskStart);
			return Math.max(0, timeRemaining)
		},
	};
	var setInactive = debounce(function(){
		remainingTime = 22;
		throttle = 66;
		minThrottle = 0;
	});

	function debounce(fn){
		var id, timestamp;
		var wait = 99;
		var check = function(){
			var last = (Date.now()) - timestamp;

			if (last < wait) {
				id = setTimeout(check, wait - last);
			} else {
				id = null;
				fn();
			}
		};
		return function(){
			timestamp = Date.now();
			if(!id){
				id = setTimeout(check, wait);
			}
		};
	}

	function abortRunning(){
		if(isRunning){
			if(lazyraf){
				cancelRequestAnimationFrame(lazyraf);
			}
			if(lazytimer){
				clearTimeout(lazytimer);
			}
			isRunning = false;
		}
	}

	function onInputorMutation(){
		if(throttle != 125){
			remainingTime = 7;
			throttle = 125;
			minThrottle = 35;

			if(isRunning) {
				abortRunning();
				scheduleLazy();
			}
		}
		setInactive();
	}

	function scheduleAfterRaf() {
		lazyraf = null;
		lazytimer = setTimeout(runTasks, 0);
	}

	function scheduleRaf(){
		lazytimer = null;
		requestAnimationFrame(scheduleAfterRaf);
	}

	function scheduleLazy(){

		if(isRunning){return;}
		throttleDelay = throttle - (Date.now() - taskStart);

		scheduleStart = Date.now();

		isRunning = true;

		if(minThrottle && throttleDelay < minThrottle){
			throttleDelay = minThrottle;
		}

		if(throttleDelay > 9){
			lazytimer = setTimeout(scheduleRaf, throttleDelay);
		} else {
			throttleDelay = 0;
			scheduleRaf();
		}
	}

	function runTasks(){
		var task, i, len;
		var timeThreshold = remainingTime > 9 ?
			9 :
			1
		;

		taskStart = Date.now();
		isRunning = false;

		lazytimer = null;

		if(runAttempts > 2 || taskStart - throttleDelay - 50 < scheduleStart){
			for(i = 0, len = tasks.length; i < len && IdleDeadline.timeRemaining() > timeThreshold; i++){
				task = tasks.shift();
				tasklength++;
				if(task){
					task(IdleDeadline);
				}
			}
		}

		if(tasks.length){
			scheduleLazy();
		} else {
			runAttempts = 0;
		}
	}

	function requestIdleCallbackShim(task){
		index++;
		tasks.push(task);
		scheduleLazy();
		return index;
	}

	function cancelIdleCallbackShim(id){
		var index = id - 1 - tasklength;
		if(tasks[index]){
			tasks[index] = null;
		}
	}

	if(!root.requestIdleCallback || !root.cancelIdleCallback){
		root.requestIdleCallback = requestIdleCallbackShim;
		root.cancelIdleCallback = cancelIdleCallbackShim;

		if(root.document && document.addEventListener){
			root.addEventListener('scroll', onInputorMutation, true);
			root.addEventListener('resize', onInputorMutation);

			document.addEventListener('focus', onInputorMutation, true);
			document.addEventListener('mouseover', onInputorMutation, true);
			['click', 'keypress', 'touchstart', 'mousedown'].forEach(function(name){
				document.addEventListener(name, onInputorMutation, {capture: true, passive: true});
			});

			if(root.MutationObserver){
				new MutationObserver( onInputorMutation ).observe( document.documentElement, {childList: true, subtree: true, attributes: true} );
			}
		}
	} else {
		try{
			root.requestIdleCallback(function(){}, {timeout: 0});
		} catch(e){
			(function(rIC){
				var timeRemainingProto, timeRemaining;
				root.requestIdleCallback = function(fn, timeout){
					if(timeout && typeof timeout.timeout == 'number'){
						return rIC(fn, timeout.timeout);
					}
					return rIC(fn);
				};
				if(root.IdleCallbackDeadline && (timeRemainingProto = IdleCallbackDeadline.prototype)){
					timeRemaining = Object.getOwnPropertyDescriptor(timeRemainingProto, 'timeRemaining');
					if(!timeRemaining || !timeRemaining.configurable || !timeRemaining.get){return;}
					Object.defineProperty(timeRemainingProto, 'timeRemaining', {
						value:  function(){
							return timeRemaining.get.call(this);
						},
						enumerable: true,
						configurable: true,
					});
				}
			})(root.requestIdleCallback)
		}
	}

	return {
		request: requestIdleCallbackShim,
		cancel: cancelIdleCallbackShim,
	};
}));