Question

So there is this function

Array.prototype.containsCaseInsensitive = function(obj) {
  var i = this.length;
  while (i--) {
    if (this[i].toUpperCase() === obj.toUpperCase()) {
      return true;
    }
  }
  return false;
}

then I create this array:

ary = [0,1,2,3];
for (item in ary){
  console.log(ary[item])
}

The output is as follows:

0
1
2
3
function(obj) {
    var i = this.length;
    while (i--) {
       if (this[i].toUpperCase() === obj.toUpperCase()) {
           return true;
       }
    }
    return false;
 }

Why is the function in the iteration?
Thanks!

Answer 1

Your property is enumerable (although you shouldn’t enumerate the keys of an array using for ... in ... anyway).

On ES5 compatible browsers you can safely add that function as a non-enumerable property using Object.defineProperty:

Object.defineProperty(Array.prototype, 'containsCaseInsensitive', {
    value: function() {
        ...
    }
});