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)">點我</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;  //結果為true  sum+=value;   });console.log(sum);  //結果為 10

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

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