javascript associative array length using jQuery

You shouldn't use an array to store non-numeric indexes, you should use a simple object:

function getObjectLength (o) {
  var length = 0;

  for (var i in o) {
    if (Object.prototype.hasOwnProperty.call(o, i)){
      length++;
    }
  }
  return length;
}

Edit: Since you are using jQuery and you want to check if the object is "empty", the 1.4 version introduced the $.isEmptyObject

if ($.isEmptyObject(obj)) { 
  //...
}

This gives you the length of your associative array:

Object.keys(testarray).length

There's no direct "length" or "size" call, you have to test the keys available within the object.

Note that all JavaScript objects are associative arrays (maps), so your code would probably be better off using a generic object rather than an array:

var testarray = {}; // <= only change is here
testarray['one'] = '1';
testarray['two'] = '2';
testarray['three'] = '3';

You can find out what the keys are in an object using for..in:

var name;
for (name in testarray) {
    // name will be 'one', then 'two', then 'three' (in no guaranteed order)
}

...with which you can build a function to test whether the object is empty.

function isEmpty(obj) {
    var name;
    for (name in obj) {
        return false;
    }
    return true;
}

As CMS flagged up in his answer, that will walk through all of the keys, including keys on the object's prototype. If you only want keys on the object and not its prototype, use the built-in hasOwnProperty function:

function isEmpty(obj) {
    var name;
    for (name in obj) {
        if (obj.hasOwnProperty(name)) {
            return false;
        }
    }
    return true;
}

I had this problem too, and I just realized the solution (and tested it in my browser):

//given: ass_arr, an associative array
//result: count now holds the "length" of ass_arr 
var count = 0;
$.each(ass_arr, function(key, val) { count+=1; } );
alert(count); //number of iterable attributes in ass_arr

Let me know if this works for you! I'm writing it right into my code like this:

var devices = STATUS.devices,
  num_devices = 0;
$.each(devices, function(id, device) { num_devices+=1; } );
//num_devices set to number of devices

You could calculate the length like below:

var testarray = {}; // Use a generic object to store non-numeric indexes not an array
testarray['one'] = '1';
testarray['two'] = '2';
testarray['three'] = '3';
var count = 0
for each(key in testarray)
 count = count + 1
alert(count); // count contains the number of items in the array

You can loop through the properties to count them:

var cnt = 0;
for (i in testarray) cnt++;
alert(cnt);

Note that the for (... in ...) will also loop items added by a prototype, so you might want to count only the items added after that:

var cnt = 0;
for (i in testarray) if (testarray.hasOwnProperty(i)) cnt++;
alert(cnt);

If you just want to check if there are any properties, you can exit out of the loop after the first item:

var empty = true;
for (i in testarray) if (testarray.hasOwnProperty(i)) { empty = false; break; }
alert(empty);

You don't really have an array there, so I'd avoid initializing it as such:

var testNotArray = { };
testNotArray['one'] = 'something';
// ...

Now this is inherently dangerous, but a first step might be:

function objectSize(o) {
  var c = 0;
  for (var k in o) 
    if (o.hasOwnProperty(k)) ++c;
  return c;
}

Again, there are a million weird ways that that approach could fail.