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HTML

              
                <h1>Public Github repos and forks at /jufa</h1>

<h2>using jQuery's promise implementation:</h2>
<ul id = "promos">
</ul>

<h2>same thing but using a standard A+ promise by wrapping with q.js:</h2>
<ul id = "promospromise">
</ul>
              
            
!

CSS

              
                body {
  font-family: sans-serif;
}

ul {
  list-style-type: none;
}
              
            
!

JS

              
                "use strict";
/**
 * Promises A+
 * inspired by: 
 * http://joseoncode.com/2013/05/23/promises-a-plus/
*/

var workingWebservice = "https://api.github.com/users/jufa/repos";
var brokenWebservice = "https://api.github.baduri";
var webserviceUnderTest;
webserviceUnderTest = workingWebservice; 
//var webserviceUnderTest = brokenWebservice; 

// so this is how we do it with jQuery callbacks and deferals:
// we use the chainable, clear, but non-standard .done() and .error()
$.ajax(webserviceUnderTest).done(function(data){
  for (var i = 0; i < data.length; i++) {
    $('#promos').append('<li><h3>'+data[i].name+'</h3><p>'+data[i].description+'</p></li>');  
  }
}).error(function(error){
    $('#promos').append('Error: ', error.state());
});

// but we want to be compliant with the Promise A+ standard 
// which is interoperable between many other asynchronous libraries.
// q.js is a popular stand-alone (not part of a bigger framework)
// implementation; we could use it to
// 'wrap'the non standard jQuery asynchronous callback scheme 
// to produce standard promises:

// first, use the Q.defer factory method to make a 'deferral' object.
// A Deferral object is a container for any asynchronous style event 
// that we want to work with using the Promises A+ standard:
var d = Q.defer();
 
// Now we have something that contains:
// a promise object we can pass around using chaining i.e. 
// doSomething.then(doSomethingElse()).then(doAThirdThing());
// a reject method - which is called if something goes wrong in this chain opf promises,
// like an timeout in a webservice call
// a resolve method - which is called when the promise returns with success and data!

//so now we tie the jQuery asynchronous callback functions .done and .error to this
// standard deferral object's reject and resolve methods, so the two together behave to the A+ standard.
// the trick here is to tie in three things:
// 1. Assign the reslt of the nonstandard jQuery asynch function to the standard promise in
//    our new deferal object
// 2. Pass the nonstandard success callback's data to the resolve method
//    our new deferal object
// 3. Pass the nonstandard error callback's data to the reject method
//    our new deferal object:
var ourNewPromise = d.promise; //Step 1 complete!
ourNewPromise = $.ajax(webserviceUnderTest)
  .done(function(data){
    d.resolve(data); //step 2 complete!
  })
  .error(function(error){
    d.reject(error); //step 3 complete!
  });


// and NOW we can handle the asynchronous result using the standard 
// Promise A+ standard notation and patterns, such as .then, intead of .done!
ourNewPromise.then(function(data){
  for (var i = 0; i < data.length; i++) {
    $('#promospromise').append('<li><h3>' + data[i].name + '</h3><p>' + data[i].description + '</p></li>'); 
  }  
}, function(error){
    console.log(error);
    $('#promospromise').append('Error: ', error.state());
});

//is this a big deal? I think it is if you are using many libraries that need to speak the same asynchronous language. The alternative is callback nesting, callbacks, and other design patterns which can make code maintenance a brace and bracket hunt!
              
            
!
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