JSON jQuery PHP

I don't understand one thing. If I want to get JSON data (key-value-pairs) from PHP to jQuery using Ajax, which of the following ones should I use?

• $.get
• $.post
• $.getJSON

Do I need to use getJSON if I want to use json_encode in a PHP file? But what if I want to send with post (there is no postJSON)?

And one more thing:

In a PHP file I wrote:

<?php
    if($_GET['value'] == "value")
    {
        $array['firstname'] = 'Johnny';
        $jsonstring=json_encode($array);
        return $jsonstring;
    }
?>

In the jQuery file:

  $.getJSON("php.php", {value: "value"}, function(data){
      alert(data.firstname);
  });

Why doesn't this work?

The problem lies with the line in PHP:

return $jsonstring;

You should echo it instead:

echo $jsonstring;

As for which jQuery method to use, I suggest $.getJSON() if you can return a pure json string. It really depends on how you use it.

When using $.getJSON(), your server file should return a JSON string. Thus echoing the string returned by json_encode() would be appropriate for the $.getJSON() method to take in the response.

You can use .ajax, this allows you to do both get and post.

I always use $.ajax.

$.ajax({
     url: "script.php",
     type: "POST",
     data: { name : "John Doe" },
     dataType: 'json',
     success: function(msg){
        alert(msg);
     }
});

in PHP:

$name = $_POST['name']
echo $name

this will alert "John Doe"

also, if it's not working, use firebug to see values being passed around.