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

Question

I get the following error in IE8:

length is null or not an object

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

Just check for the object being null or empty:

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

C'mon gang this was glaringly obvious :-)

Answer 2

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.