How to Create JSONP Callbacks in JavaScript for Cross-Domain Requests?

Creating JSONP Callbacks in JavaScript

Cross-domain requests can pose a challenge in JavaScript development. However, JSONP (JSON with Padding) provides a solution to this issue.

Modifying Your JSON API for JSONP

To enable JSONP capabilities in your JSON API, follow the simple steps below:

1. Accept a "callback" Parameter in the GET Request:

   if(array_key_exists('callback', $_GET)){

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2. Wrap the Callback Function Around Your Data:

   $callback.'('.$data.');';

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Using PHP as an example, the code below demonstrates these steps:

<code class="php"><?php

$data = '{}'; // json string

if(array_key_exists('callback', $_GET)){

    header('Content-Type: text/javascript; charset=utf8');
    header('Access-Control-Allow-Origin: http://www.example.com/');
    header('Access-Control-Max-Age: 3628800');
    header('Access-Control-Allow-Methods: GET, POST, PUT, DELETE');

    $callback = $_GET['callback'];
    echo $callback.'('.$data.');';

}else{
    // normal JSON string
    header('Content-Type: application/json; charset=utf8');

    echo $data;
}
?></code>

Using the JSONP Service

To utilize the JSONP service, you can employ the HTML script tag:

<code class="html"><script>
    function receiver(data){
        console.log(data);
    }
</script>

<script src="data-service.php?callback=receiver"></script></code>

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