CODEWITHSUNDEEP
javascriptiterator
obelia
obelia

Reputation: 2145

Javascript Object iterate method?

Javascript doesn't have a general object iterator, to allow something like:

foo.iterate (function (key, value) {
    console.log ("key->" + key + " value->" + value);
});

Seems convenient and trivial to implement. Is something like this built in to any popular libraries? I don't want to reinvent the wheel, and if do something like this would like to follow naming (and semantic) conventions for any existing method.

So does a general iterator like this exist somewhere?

added: I've been tinkering around and added an iterator function to Object.prototype. This slowed down the for loop by a factor of about 20! I wasn't even calling the new iterator method, just adding it to Object's prototype greatly slowed down for loops. I'm assuming this negates an optimization in Chrome. This would explain why none of these libraries mentioned add an iteration method to Object.

Upvotes: 0

Views: 1729

Answers (4)

Barmar
Barmar

Reputation: 780655

You can use for-in, but you need to add extra code to distinguish properties of the object itself from those inherited from a prototype:

Object.prototype.iterate = function(callback) {
    for (var key in this) {
        if (this.hasOwnProperty(key)) {
             callback(key, this[key]);
        }
    }
}

Every object now has an iterate() method since we've attached this function to the Object prototype. Now, you can use the code example from the OP to iterate over the properties of the object foo.

Note: there are NO "classes" in Javascript, and functions are first class data types. So, any functions or "methods" added to the object will be iterated over using this function as well.

Upvotes: 2

Rustavore
Rustavore

Reputation: 1885

Yes! Most popular libraries implement some form of this. Here's a few examples:

  1. jQuery.each(). Here's an example:

    $.each([ 52, 97 ], function( index, value ) { alert( index + ": " + value ); });

  2. Underscore _.each(). Here's an example of this one:

    _.each([1, 2, 3], alert);

  3. Dojo Toolkit's forEach()

  4. Apparently, Javascript 1.7 has an iterator built in

  5. See also the Prototype framework's Enumerable, albeit a bit dated.

I would highly recommend underscore for it's wide variety of utility methods to make manipulating JavaScript objects and arrays easy, even for more sophisticated operations. This has the advantage of working client and server side without having lots of DOM manipulation functionality built-in like jQuery, Dojo, and Prototype.

If you're looking to implement a simple version of each() for arrays, checkout the functional programming chapter in Eloquent Javascript and his implementation:

function forEach(array, action) {
  for (var i = 0; i < array.length; i++)
    action(array[i]);
}

forEach(["Wampeter", "Foma", "Granfalloon"], print);

Upvotes: 1

Sushanth --
Sushanth --

Reputation: 55740

Why not a simple for in loop ?

for(var key in obj) {
     console.log ("key->" + key + " value->" + obj[key]);
}

Upvotes: 1

elclanrs
elclanrs

Reputation: 94101

It doesn't, but here's a way to do it without libraries or extra functions (other than for..in loop):

Object.keys(foo).forEach(function(key){
  console.log(this[key]);
}, foo);

Upvotes: 4

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