js常见遍历操作小结

本文实例讲述了js常见遍历操作。分享给大家供大家参考，具体如下：

for循环

var a = new Array("first", "second", "third") 
for(var i = 0;i < a.length; i++) {
document.write(a[i]+",");
}

for in

var arr = new Array("first", "second", "third") 
for(var item in arr) {
document.write(arr[item]+",");
}

for each

<button onclick="numbers.forEach(myFunction)">点我</button>
<p id="demo"></p>
<script>
demoP = document.getElementById("demo");
var numbers = [4, 9, 16, 25];
function myFunction(item, index) {
  demoP.innerHTML = demoP.innerHTML + "index[" + index + "]: " + item + "<br>"; 
}
</script>

var arr = [1,2,3,4];
arr.forEach(function(value,index,array){
  array[index] == value;  //结果为true
  sum+=value; 
  });
console.log(sum);  //结果为 10

each

$.each([],function(index,value,array){
　//code something
　})

map

[].map(function(value,index,array){
//code
})

感兴趣的朋友可以使用在线HTML/CSS/JavaScript代码运行工具：http://tools.3water.com/code/HtmlJsRun测试上述代码运行效果。