HTTP Content-Type Header and JSON

I have always been trying to avoid using most of the HTTP protocol’s properties for the sake of fear of the unknown.

However, I said to myself that I’m going to face fear today and start using headers purposefully. I have been trying to send json data to the browser and use it right away. For example, if I have an Ajax handler function on ready state 4 which looks like so:

function ajaxHandler(response){
    alert(response.text);
}

And I have set the content-type header in my PHP code:

header('Content-Type: application/json');
echo json_encode(array('text' => 'omrele'));

Why can’t I directly access the property from the handler function, when the browser is clearly told that the incoming data is application/json?

Answer

The Content-Type header is just used as info for your application. The browser doesn’t care what it is. The browser just returns you the data from the AJAX call. If you want to parse it as JSON, you need to do that on your own.

The header is there so your app can detect what data was returned and how it should handle it. You need to look at the header, and if it’s application/json then parse it as JSON.

This is actually how jQuery works. If you don’t tell it what to do with the result, it uses the Content-Type to detect what to do with it.