What is AJAX and Why Should I Care?

    // AJAX = Asynchronous JavaScript and XML
    // none of these examples do proper error handling of
    // nasty http status codes or
    // invalid data types – text, xml, json, etc
    
    // ***************************************************
    // Old version of AJAX
    var xhr = new XMLHttpRequest( );
    xhr.open('GET', uri, true); // true here means asynchronous call (user can still interact with site, while waiting for request to come back)
    xhr.addEventListener('load', function(response){
        //handle the response from the server
        var data = response.responseText; // responseXML 
        var json = JSON.parse(data); // JSON object
        console.log('XMLHttpRequest : ', data) ;
    });
    xhr.addEventListener('error', function(err){
        //error handling network request
    })
    xhr.send(null);
    
    //***************************************************
    // New version of AJAX 
    fetch(uri)
    .then(function(response){ 
        return response.json( );
    })
    .then(function(data){ 
        console.log(data); 
    });
    .catch(function(err){
        // error handling network request
    })