js常见遍历操作小结

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

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

<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([],function(index,value,array){
　　　//code something
　})

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