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up vote 2 down vote favorite

This question already has an answer here:

I have the following:

var tags = ["Favorite", "Starred", "High Rated"];

for (var tag in tags) {
    console.log(tag);
}

Output is

0
1
2

I'd like it to output:

Favorite
Starred
High Rated

How do I do this? Thanks.

share|improve this question

marked as duplicate by Fabrício Matté, nice ass, Joe, Apurv, Avadhani Y Jul 6 '13 at 13:01

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.
3  
console.log(tags[tag]) –  nice ass Jul 6 '13 at 2:12
    
@onetrickpony this worked. Please submit as answer and I'll mark as correct. Thanks. –  Steven Jul 6 '13 at 2:15

2 Answers 2

up vote 6 down vote accepted

Itearting over an array:

That's an array of strings, don't use for..in, use the vanilla for loop:

var tags = ["Favorite", "Starred", "High Rated"];
for (var i = 0; i < tags.length; i++) { // proper way to iterate an array
    console.log(tags[i]);
}

Output:

Favorite
Starred
High Rated

Proper usage of for..in:

It is meant for object's properties, like:

var tags2 = {"Favorite": "some", "Starred": "stuff", "High Rated": "here"};
for (var tag in tags2) { // enumerating objects properties
    console.log("My property: " + tag +"'s value is " +tags2[tag]);
}

Output:

My property: Favorite's value is some
My property: Starred's value is stuff
My property: High Rated's value is here

Side effects of for..in with arrays:

Don't take my word for it, let's see why not use it: for..in in arrays can have side effects. Take a look:

var tags3 = ["Favorite", "Starred", "High Rated"];
tags3.gotcha = 'GOTCHA!'; // not an item of the array

// they can be set globally too, affecting all arrays without you noticing:
Array.prototype.otherGotcha = "GLOBAL!";

for (var tag in tags3) {
    console.log("Side effect: "+ tags3[tag]);
}

Output:

Side effect: Favorite
Side effect: Starred
Side effect: High
Side effect: GOTCHA!
Side effect: GLOBAL!

See a demo fiddle for these codes.

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1  
+1 for object's properties usage –  Vassilen Dontchev Jul 6 '13 at 2:19
up vote 0 down vote

Using in in for loops in JavaScript is not like : in Java or foreach in other languages - instead of providing reference to the element, it provides its index. If you use a framework like jQuery, there is a method - $.each which gives access to the element (not only the index) via callback when iterating: 

var a = ["Favorite", "Starred", "High Rated"];
$.each ( a, function ( index, data ) 
{
   console.log ( data );
});
share|improve this answer
    
Why would you use jQuery just to iterate over an array? –  Blender Jul 6 '13 at 2:21
    
That's not true. for..in does NOT return the index, but the properties of the object. If you use an array the properties are it's indexes, but if you use an object you'll get a different output (e.g: var person = { name: 'John', age: 25 }; for(var c in person ) { console.log(c); }). I also wouldn't use jQuery for iterating through a list. Using native javascript is way more performatic . –  Marlon Bernardes Jul 6 '13 at 2:22

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