Javascript : array.length returns undefined

Question

I have a set of data that is being passed on by the PHP's json_encode function. I'm using the jQuery getJSON function to decode it:

$.getJSON("url", function (data) {
    console.log(data);
});

The output looks like this in the console:

Object {1: Object, 2: Object, 3: Object, 4: Object, 5: Object, 6: Object, 7: Object, 8: Object, 9: Object, 10: Object}

I can access each array by using data[1], data[2] etc, but to make it easier I thought of looping thought it so I can access all at once:

$.getJSON("url", function (data) {
    for (var i = 0, len = data.length; i < len; i++) {
        //do something
    }
});

However I can't get this to work because the data.length returns the value undefined. What is wrong and how can I fix it?

That isn't an array. It is an object. You can't loop through objects like you can arrays. — Jeff Shaver, Feb 04 '14 at 12:21
Looks as though it's not an array but an arbitrary object. If you have control over the PHP serialization, you might be able to change that. — Scott Sauyet, Feb 04 '14 at 12:22
+1 to what Scott said: it's quite easy to turn this into a real array, replacing your `json_encode($something)` with `json_encode(array_values($something))`. — raina77ow, Feb 04 '14 at 12:25
@ScottSauyet if you can post that as an answer I can mark it as correct — rksh, Feb 05 '14 at 14:49
@rksh: I know this is an old question, but I was wondering if you could have a look at it again, in regards to the accepted answer ;-) — Cerbrus, Oct 17 '17 at 06:59

Cerbrus · Answer 1 · 2014-02-04T12:28:27.887

89

Objects don't have a .length property.

A simple solution if you know you don't have to worry about hasOwnProperty checks, would be to do this:

Object.keys(data).length;

If you have to support IE 8 or lower, you'll have to use a loop, instead:

var length= 0;
for(var key in data) {
    if(data.hasOwnProperty(key)){
        length++;
    }
}

edited Feb 04 '14 at 12:28

answered Feb 04 '14 at 12:21

Cerbrus

70,800
18
132
147

1

for [IE >= 9](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/keys#Browser_compatibility) – Arun P Johny Feb 04 '14 at 12:23

score 30 · Answer 2 · edited Jul 25 '16 at 17:07

30

One option is:

Object.keys(myObject).length

Sadly it not works under older IE versions (under 9).

If you need that compatibility, use the painful version:

var key, count = 0;
for(key in myObject) {
  if(myObject.hasOwnProperty(key)) {
    count++;
  }
}

edited Jul 25 '16 at 17:07

Sam

1,264
14
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answered Feb 04 '14 at 12:24

ragklaat

926
5
12

saved me a great time after all those years, thanks! – msc May 05 '23 at 09:08

score 7 · Answer 3 · edited May 23 '17 at 12:10

It looks as though it's not an array but an arbitrary object. If you have control over the PHP serialization, you might be able to change that.

As raina77ow pointed out, one way to do this in PHP would be by replacing something like this:

json_encode($something)

with something like:

json_encode(array_values($something))

But don't ignore the other answers here about Object.keys. They should also accomplish what you want if you don't have the ability or the desire to change the serialization of your object.

score 2 · Answer 4 · answered Feb 04 '14 at 12:23

2

try this

Object.keys(data).length

If IE < 9, you can loop through the object yourself with a for loop

var len = 0;
var i;

for (i in data) {
    if (data.hasOwnProperty(i)) {
        len++;
    }
}

answered Feb 04 '14 at 12:23

Linga

10,379
10
52
104

score 1 · Answer 5 · answered Oct 13 '18 at 19:11

1

An easy fix to this question is to add '[' in the start of your json file, and ending it with a ']'. This solved it for me.

answered Oct 13 '18 at 19:11

Nikolaj Egelund Jørgensen

17
1
5

Javascript : array.length returns undefined

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