Answer 1

excutor执行器里面是同步执行的，then里面是异步操作

如何体现呢？能举例说明吗？

Answer 2

 function each(obj, callback) {
	    var i = 0;
	    var length = obj.length
	    for (; i < length; i++) {
	        value = callback(i, obj[i]);
	    }
	}
     
     function eachWithCall(obj, callback) {
	    var i = 0;
	    var length = obj.length
	    for (; i < length; i++) {
	        value = callback.call(obj[i], i, obj[i]);
	    }
	}
     
     function eachWithApply(obj, callback) {
     	var i = 0;
     	var length = obj.length;
     	for(; i < length; i ++) {
     		value = callback.apply(obj[i], [i,obj[i]]);
     	}
     }
     
     var arr = Array.from({length: 10000000}, (v, i) => i)
	 
	    console.time('each')
		var i = 0;
		each(arr, function(index, item){
		    i += item;
		})
		console.timeEnd('each')
		
		
		console.time('eachWithCall')
		var j = 0;
		eachWithCall(arr, function(index, item){
		    j += item;
		})
		console.timeEnd('eachWithCall')
		
		console.time('eachWidthApply')
		var i = 0;
		each(arr, function(index, item){
		    i += item;
		})
		console.timeEnd('eachWidthApply')
		
		//each: 815.879150390625ms
		//eachWithCall: 308.455078125ms
		//eachWidthApply: 828.31591796875ms

这里我的打印的each比eachWithCall慢？？？，博主能给我说说吗？