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
– Jeff Shaver, Commented Feb 4, 2014 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
– Scott Sauyet, Commented Feb 4, 2014 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
– raina77ow, Commented Feb 4, 2014 at 12:25

Cerbrus · Accepted Answer · 2014-02-04 12:28:27Z

91

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 4, 2014 at 12:28

answered Feb 4, 2014 at 12:21

Cerbrus

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1 Comment

Arun P Johny Over a year ago

for IE >= 9

Sam · Accepted Answer · 2016-07-25 17:07:38Z

32

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, 2016 at 17:07

Sam

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answered Feb 4, 2014 at 12:24

ragklaat

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1 Comment

msc Over a year ago

saved me a great time after all those years, thanks!

Community · Accepted Answer · 2017-05-23 12:10:34Z

7

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.

edited May 23, 2017 at 12:10

CommunityBot

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answered Feb 7, 2014 at 14:36

Scott Sauyet

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Comments

Linga · Accepted Answer · 2014-02-04 12:23:43Z

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 4, 2014 at 12:23

Linga

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Comments

Nikolaj Egelund Jørgensen · Accepted Answer · 2018-10-13 19:11:08Z

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, 2018 at 19:11

Nikolaj Egelund Jørgensen

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