1、测试目的：对比JS 中for、while、for in、for of、for each效率 2、测试环境： Node环境和Chrome浏览器环境 3、测试方法：分别使用上述待测接口遍历数组

var arr = []
console.time(write array)
for (var i = 0; i < 1000 * 1000; i++) {
          
   
    arr.push(i)
}
console.timeEnd(write array)

console.time(for loop read)
var sum0 = 0
for (var j = 0; j < 1000 * 1000; j++) {
          
   
    sum0 += arr[j]
}
console.timeEnd(for loop read)

console.time(while read)
var sum1 = 0, index = 0
while (index < 1000 * 1000) {
          
   
    sum1 += arr[index]
    index++
}
console.timeEnd(while read)

console.time(for in read)
var sum2 = 0
for (let key in arr) {
          
   
    sum2 += arr[key]
}
console.timeEnd(for in read)

console.time(for of read)
var sum3 = 0
for (let value in arr) {
          
   
    sum3 += value
}
console.timeEnd(for of read)

console.time(for each read)
var sum4 = 0
arr.forEach(function (item) {
          
   
    sum4 += item
})
console.timeEnd(for each read)

测试结果： Node环境结果如下：

Chrome浏览器环境结果如下：

结论：

a)、for与while效率相差无几 b)、for > for each > for in > for of