Copy an associative array in JavaScript

In JavaScript, associative arrays are called objects.

<script>
    var some_db = {
       "One" : "1",
       "Two" : "2",
       "Three" : "3"
    };

    var copy_db = clone(some_db);

    alert(some_db["One"]);

    alert(copy_db["One"]);

    function clone(obj) {
        if (null == obj || "object" != typeof obj) return obj;
        var copy = obj.constructor();
        for (var attr in obj) {
            if (obj.hasOwnProperty(attr)) copy[attr] = clone(obj[attr]);
        }
        return copy;
    }
</script>

I would normally use var copy_db = $.extend({}, some_db); if I was using jQuery.

Fiddle Proof: http://jsfiddle.net/RNF5T/

Thanks @maja.

As @Niko says in the comment, there aren't any associative arrays in JavaScript.

You are actually setting properties on the array object, which is not a very good idea. You would be better off using an actual object.

var some_db = {};
some_db["One"] = "1";
some_db["Two"] = "2";
some_db["Three"] = "3";

var copy_db = {}, prop;
// Loop over all the keys in the object
for (prop in some_db) {
  // Make sure the object has this value, and not its prototype
  if (some_db.hasOwnProperty(prop)) {
    copy_db[prop] = some_db[prop];
  }
}

Many libraries implement an extend function which does exactly this (copy keys from one object to another). Most notably jQuery and Underscore.js. Underscore.js also has _.clone(obj) which is effectively _.extend( {}, obj )

If you want to use JSON, you can take this 'associative array' object:

var assArray = {zero:0, one:1, two:2, three:3, what:'ever', you:'want'};

And 'clone' it like this:

var clonedObj = JSON.parse(JSON.stringify(assArray));