Why is my JSON object undefined?

Question

I'm trying to parse a JSON data structure but what I think should be data is returning undefined.

Here is the jQuery I'm using:

....
var messages = data.messages;

$.each(messages, function(i, val) {

    var user = messages[i];

    //console.log(user);
    console.log(user['msg']);

});

The PHP data structure look like this:

...
$message_info = array();

$message_info[$row['username']]['prvt'] = 1;
$message_info[$row['username']]['msg'] = stripslashes($row['message']);
$message_info[$row['username']]['ts'] = $row['timestamp'];

...

$message_list[] = $message_info;

...

$res->messages = $message_list;
echo json_encode($res);

If I dump user to the console the output look like this:Object

{john: Object}
  john: Object
  msg: "test msg"
  prvt: 0
  ts: "2012-12-10 09:16:13"

This is what data looks like in the console:

Object {success: true, lastid: "60", messages: Array[15]}
lastid: "60"
messages: Array[15]
  0: Object
    john: Object
      msg: "test msg"
      prvt: 0
      ts: "2012-12-10 09:16:13"
  1: Object
    john2: Object
      msg: "test msg2"
      prvt: 1
      ts: "2012-12-10 09:18:13"
 ...

Any idea why I can't access and retrieve the contents of msg?

try with echo json_encode($message_list,JSON_FORCE_OBJECT); — xkeshav
– xkeshav, Commented Dec 10, 2012 at 20:39
And if the above doesn't work a console.log(data) right after you get the data variable might help. Note also that you don't need user = messages[i] because the val parameter will already be set to messages[i]. — nnnnnn
– nnnnnn, Commented Dec 10, 2012 at 20:40
Are you getting this JSON using AJAX? Are you trying to access the data before the AJAX callback is complete? — Blazemonger
– Blazemonger, Commented Dec 10, 2012 at 20:44

Blazemonger · Accepted Answer · 2012-12-10 20:55:18Z

1

Rewrite your PHP to avoid nesting msg inside of $row['username']:

$message_info = array();
$message_info['username'] = $row['username']; // find this in JS with user['username']
$message_info['prvt'] = 1;
$message_info['msg'] = stripslashes($row['message']);
$message_info['ts'] = $row['timestamp'];

With that change, your JavaScript should work as-is.

answered Dec 10, 2012 at 20:55

Blazemonger

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3 Comments

Paul Over a year ago

That worked but I still don't understand why I couldn't reference the username as the key...

Blazemonger Over a year ago

Because the username is different each time, making it impossible for you to write code to access the data underneath it. If you want to user a username to locate data, loop through the array and test if user['username'] equals a given string.

Paul Over a year ago

Thanks, I guess I was making more difficult then it had to be. Thanks again!

Julien May · Accepted Answer · 2012-12-10 20:53:06Z

0

your user objects contains an object that is referenced by the key "john", "john2" etc.

user.john.msg or user.john2.msg

should work.

Therefore to build a more generic json structure in php, i would do the following:

...
$message_info['user']['name'] = $row['username'];
$message_info['user']['prvt'] = 1;
...

answered Dec 10, 2012 at 20:53

Julien May

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1 Comment

Paul Over a year ago

The username could be anything so I can make a static call like that

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