'length' is null or not an object? IE 8

Question

Hey guys quick question I get the following error 'length is null or not an object' in IE 8, anyone have any ideas? Feedback greatly appreciated...

 function refresh() {
$.getJSON(files+"handler.php?action=view&load=update&time="+lastTimeInterval+"&username="+username+"&topic_id="+topic_id+"&t=" + (new Date()), function(json) {
    if(json.length) {
      for(i=0; i < json.length; i++) {
        $('#list').prepend(prepare(json[i]));
        $('#list-' + count).fadeIn(1500);
      }
      var j = i-1;
      lastTimeInterval = json[j].timestamp;
    }
  });

}

Answer 1

A JSON is an object, you seem to be treating it like an array. Does it really have a length property? Show us the JSON?

You might need to use a for..in instead.

EDIT: Can you make the JSON from the backend structure like so?

({
    "foo": [] 
})

Answer 2

What does your returned JSON look like? If you're returning an object, length might not be explicitly defined, whereas if you're returning an array, it should be defined automatically.

Answer 3

First thing that comes to mind is that length is not a property of whatever json is. What is the json variable supposed to be anyway?

Answer 4

JSON objects (returned by jQuery or otherwise) do not have a length property. You'll need to iterate over the properties, most likely, or know the structure and simply pull out what you want:

$.getJSON( ..., ..., function( json ) {
  for( var prop in json ) {
    if( !json.hasOwnProperty( prop ) ) { return; }
    alert( prop + " : " + json[prop] );
  }
} );

Alternatively, grab a library like json2 and you'll be able to stringify the object for output/debugging.

Answer 5

pop the JSON in a span then clip it and paste it here so we can see it:

<span id="JSObject2">empty</span>

with the json2.js from here: (link for it at bottom of the page) http://www.json.org/js.html

myJSON = JSON.stringify(json);
$('#JSObject2').text(myJSON);

Using that, we can help you better, and you can see what you have!

Answer 6

Just check for the object being null or empty:

if (json && json.length) {
  // ...
}

C'mon gang this was glaringly obvious :-)