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

There are two ways to traverse JS arrays:

The first one: 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]+",");

}

The output result: fitst, second, third

The first way: use for...in this way of traversal, for example:

?

var arr = new Array("first", "second", "third")

for(var item in arr ) {

document.write(arr[item]+",");

}

Output results: fitst, second, third