Perform curl request in javascript?

You can use JavaScripts Fetch API (available in your browser) to make network requests.

If using node, you will need to install the node-fetch package.

const url = "https://api.wit.ai/message?v=20140826&q=";

const options = {
  headers: {
    Authorization: "Bearer 6Q************"
  }
};

fetch(url, options)
  .then( res => res.json() )
  .then( data => console.log(data) );

curl is a command in linux (and a library in php). Curl typically makes an HTTP request.

What you really want to do is make an HTTP (or XHR) request from javascript.

Using this vocab you'll find a bunch of examples, for starters: Sending authorization headers with jquery and ajax

Essentially you will want to call $.ajax with a few options for the header, etc.

$.ajax({
        url: 'https://api.wit.ai/message?v=20140826&q=',
        beforeSend: function(xhr) {
             xhr.setRequestHeader("Authorization", "Bearer 6QXNMEMFHNY4FJ5ELNFMP5KRW52WFXN5")
        }, success: function(data){
            alert(data);
            //process the JSON data etc
        }
})

Yes, use getJSONP. It's the only way to make cross domain/server async calls. (*Or it will be in the near future). Something like

$.getJSON('your-api-url/validate.php?'+$(this).serialize+'callback=?', function(data){
if(data)console.log(data);
});

The callback parameter will be filled in automatically by the browser, so don't worry.

On the server side ('validate.php') you would have something like this

<?php
if(isset($_GET))
{
//if condition is met
echo $_GET['callback'] . '(' . "{'message' : 'success', 'userID':'69', 'serial' : 'XYZ99UAUGDVD&orwhatever'}". ')';
}
else echo json_encode(array('error'=>'failed'));
?>