Javascript "unique()" function

Question

I added unique() function to Javascript Array:

Array.prototype.unique = function(){
  return this.filter(function(item, ind, arr){
    return ind == arr.lastIndexOf(item);
  });
};

but when I iterate like this:

for (i in arr) { ... }

i becomes unique as well:

var arr = [1, 2, 1];
for (i in arr) {
    console.log(i + " ===> " + arr[i]);
}

// 0 ===> 1
// 1 ===> 2
// 2 ===> 1
// unique ===> function () { return this.filter(function (item, ind, arr) {return ind == arr.lastIndexOf(item);}); }

I know that I can iterate like this:

for (i = 0; i < arr.length; i++) { ... }

However, I still wonder if it's possible to add functions to Array and iterate like this:

for (i in arr) { ... }

?

you should not use for in when operating with an array stackoverflow.com/a/6974628/575527 — Joseph
– Joseph, Commented Mar 18, 2012 at 11:26
Similar: Javascript custom Array.prototype interfering with for-in loops, JavaScript “For …in” with Arrays — minopret
– minopret, Commented Mar 18, 2012 at 11:36

taskinoor · Accepted Answer · 2012-03-18 11:33:16Z

5

You can make the unique property non-enumerable.

Object.defineProperty(Array.prototype, "unique", { enumerable : false,
                                                  configurable : true});

answered Mar 18, 2012 at 11:33

taskinoor

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