for..in loop loops over non-numeric indexes “clean” and “remove”

Question

This is something very basic I might be missing here but I haven\'t seen such result till now.

I have a for loop where options.headers.length is 3. And in

Answer 1

1. don use just index (as that is = window.index = global = bad) use var index (read more here https://www.google.pl/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=globals+javascript+bad)

2. you have to check does the array has it as own property or maybe its some function (more after answer)

---

for (var index in options.headers) {
    if (options.headers.hasOwnProperty(index) {
         // code here
    }
}

more about #2:

let's say we have

var array = [0,1,2,3];

and besides that, extending array with function (arrays can have functions in javascript and strings too)

Array.prototype.sayHello = function() {
    alert('Hello');
};

then your loop would print sayHello as part of the array, but that's not it's own property, only the arrays