for循环效率对比

三种for循环

for(var i = 0;i < arr.length;i++){
console.log(arr[i]);
}

for(var i = 0,len = arr.length;i < len;i++){
console.log(arr[i]);
}

fir(var i in arr){
console.log(arr[i]);
}

时间对比

function test1(){
var arr = new Array(1000000);
var date1 = new Date();
for(var i =0;i<arr.length;i++){
arr[i]=0;
}
var date2 = new Date();
for(var i =0,j=arr.length;i<j;i++){
arr[i]=1;
}
var date3 = new Date();
for(var i in arr){
arr[i]=2;
}
var date4 = new Date();
var for1_time = (date2 - date1);
var for2_time = (date3 - date2);
var for3_time = (date4 - date3);
console.log(for1_time); //Firefox:10   Chrome:34
console.log(for2_time); //Firefox:4    Chrome:5
console.log(for3_time); //Firefox:750  Chrome:516
}
test1();

结论

for-in