JS array traversal methods for loops and for...in

There are two ways to traverse JS arrays:

The first type: a general for loop, for example:

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

Output result: fitst, second, third

The first one: use for...in to traverse, for example:

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

Output result: fitst, second, third