[jquery] How to parse JSON array in jQuery?

EDIT I checked the jQuery documentation and using $.ajax with the json datatype specified returns an evaluated javascript object, so eval() isn't the answer here. I knew that anyway, since I am able to parse single JSON objects, just not arrays. The problem is the $.each-ing my way through them :)

I have followed the syntax for parsing a JSON array in jQuery to the letter, but it doesn't work for some reason. I am fetching the array using $.ajax, have specified the correct datatype, and in Firebug can see that the response from my PHP script is []. Yet when I try to use $.each to iterate through the array, all I get is undefined values when I try to console.log various parts of the array. Here is where my php script makes and encodes the array:

if(mysqli_num_rows($new_res) > 0) {
$messages = array();

while($message_data = mysqli_fetch_assoc($query_res)) {
  $message = array(
    'poster' => $message_data['poster'],
    'message' => $message_data['message'],
    'time' => $message_data['time']
  );

  $messages[] = $message;
}

echo json_encode($messages);
} else if(mysqli_num_rows($new_res) == 0) {
$message = array(
  'poster' => '',
  'message' => 'No messages!',
  'time' => 1
);

echo json_encode($message);
}

And here is my attempt to parse it:

   var logged_in = '<?php echo $logged_in; ?>';
   var poster = '<?php echo $_SESSION["poster"];?>';
     $.ajax({
     url: 'do_chat.php5',
     type: 'post',
     data: ({'poster':poster,'logged_in':logged_in}),
     dataType: 'json',
     success: function(data) {
         $.each(data, function(messageIndex, message) {
                    console.log(parseInt($('#chatWindow :last-child > span').html())+' '+message['time']);
       if((parseInt(message['time']) > parseInt($('#chatWindow :last-child > span').html()))) {
     $('#chatWindow').append('<div class="poster">'+message['poster']+'</div><div class="message"><span>'+message['time']+'</span>'+message['message']+'</div>');
       }
       });
     }
     });

Without the $.each function I am able to successfully parse single JSON objects, but not an array. This is my first outing with JSON and $.each, and I'm pretty new to jQuery, so go easy if my code has ugly bits!

I am trying to parse JSON data returned from an ajax call, and the following is working for me:

Sample PHP code

$portfolio_array= Array('desc'=>'This is test description1','item1'=>'1.jpg','item2'=>'2.jpg');

echo json_encode($portfolio_array);

And in the .js, i am parsing like this:

var req=$.post("json.php", { id: "" + id + ""},
function(data) {
    data=$.parseJSON(data);
    alert(data.desc);
    $.each(data, function(i,item){
    alert(item);
    });
})
.success(function(){})
.error(function(){alert('There was problem loading portfolio details.');})
.complete(function(){});

If you have multidimensional array like below

$portfolio_array= Array('desc'=>'This is test description 1','items'=> array('item1'=>'1.jpg','item2'=>'2.jpg'));
echo json_encode($portfolio_array);

Then the code below should work:

var req=$.post("json.php", { id: "" + id + 
    function(data) {
    data=$.parseJSON(data);
    alert(data.desc);
    $.each(data.items, function(i,item){
    alert(item);
    });
})
.success(function(){})
.error(function(){alert('There was problem loading portfolio details.');})
.complete(function(){});

Please note the sub array key here is items, and suppose if you have xyz then in place of data.items use data.xyz

jQuery.parseJSON - new in jQuery 1.4.1

You can download a JSON parser from a link on the JSON.org website which works great, you can also stringify you JSON to view the contents.

Also, if you're using EVAL and it's a JSON array then you'll need to use the following synrax:

eval('([' + jsonData + '])');

You can use the Javascript eval() function to parse the JSON for you. See the JSON website for a better explanation, but you should be able to change your success function to...

var returnedObjects = eval(data);
var i = 0;
for (i = 0; i < returnedObjects.length; i++){
    console.log('Time: ' + returnedObjects[i].time);
}

...or something close.

No, with eval is not safe, you can use JSON parser that is much safer: var myObject = JSON.parse(data); For this use the lib https://github.com/douglascrockford/JSON-js

Using .NET 3.5 FIX

All of you are slightly wrong, but the combination of all of your efforts has paid off!

Instead of eval('([' + jsonData + '])'); do

success: function(msg){
var data = eval(msg.d);
var i=0;
for(i=0;i<data.length;i++){
    data[i].parametername /// do whatever you want here.
};

I don't know anything about the whole "don't use eval," but what I do know is that by doing the '([' + msg + '])' you are nesting those objects deeper, instead of up a level.

I know this is pretty long after your post, but wanted to post for others who might be experiencing this issue and stumble across this post as I did.

It seems there's something about jquery's $.each that changes the nature of the elements in the array.

I wanted to do the following:

$.getJSON('/ajax/get_messages.php', function(data) {

    /* data: 

    [{"title":"Failure","details":"Unsuccessful. Please try again.","type":"error"},
    {"title":"Information Message","details":"A basic informational message - Please be aware","type":"info"}]

    */

    console.log ("Data0Title: " + data[0].title);
    // prints "Data0Title: Failure"

    console.log ("Data0Type: " + data[0].type);
    // prints "Data0Type: error"

    console.log ("Data0Details: " + data[0].details);
    // prints "Data0Details: Unsuccessful. Please try again"


    /* Loop through data array and print messages to console */

});

To accomplish the loop, I first tried using a jquery $.each to loop through the data array. However, as the OP notes, this doesn't work right:

$.each(data, function(nextMsg) {    
    console.log (nextMsg.title + " (" + nextMsg.type + "): " + nextMsg.details);
    // prints 
    // "undefined (undefined): undefined
    // "undefined (undefined): undefined
});

This didn't exactly make sense since I am able to access the data[0] elements when using a numeric key on the data array. So since using a numerical index worked, I tried (successfully) replacing the $.each block with a for loop:

var i=0;
for (i=0;i<data.length;i++){
    console.log (data[i].title + " (" + data[i].type + "): " + data[i].details);
    // prints
    // "Failure (error): Unsuccessful. Please try again"
    // "Information Message (info): A basic informational message - Please be aware"
}

So I don't know the underlying problem, a basic, old fashioned javascript for loop seems to be a functional alternative to jquery's $.each

Careful with the eval, the JSON specs http://json.org/js.html recommend something like

var myObject = eval('(' + myJSONtext + ')');

And there may be some more gotchas. There is a plugin for jQuery that will take care of it, i guess:

http://code.google.com/p/jquery-json/

Do NOT eval. use a real parser, i.e., from json.org

Your data is a string of '[{}]' at that point in time, you can eval it like so:

function(data) {
    data = eval( '(' + data + ')' )
}

However this method is far from secure, this will be a bit more work but the best practice is to parse it with Crockford's JSON parser: https://github.com/douglascrockford/JSON-js

Another method would be $.getJSON and you'll need to set the dataType to json for a pure jQuery reliant method.