calling Json data returns undefined "

Question

When I call json object from php file it returns undefined. I can see all data writing alert(data) but when I write alert(data.books) it returns undifined.

$JSON = '

{
  "books": {
 "book1": "firstbook",
 "book2": "secondbook"
  }
  }
';

and I call it with jquery

jQuery('#login').live('submit',function(event) {


$.ajax({
    url: 'lib/login.php',
    type: 'POST',
    dataType: 'json',
    data: $('#login').serialize(),
  success: function(data ) {

alert(' ' +data.books);

  if(data.books.book1){  
alert("OK"); 
}else
{
alert("error");   
}
}

 });

   return false;


});

EDIT This is how it returns alert(data)

    {

  "books": {

  "book1": "firstbook",

  "book2": "secondbook"

}

}

Answer 1

If you're on jQuery 1.4+, the JSON you're returning isn't valid, it needs a set of quotes around the first books entry, like this:

{
  "books": {
    "book1": "firstbook",
    "book2": "secondbook"
  }
}

Earlier versions are more lenient about this, but once you correct it, alert(data.books) should result in an object alert. For your if(), you'd use data.books.book1 to get the entry in the JSON as it is now.

Answer 2

I changed in .php file like

$arr = array ( "book1" => "firstbook" ,"book2" => "secondbook" );

now it shows when i write alert(data.book1) out put fisrtbook .for checking if(data.book1) it works.