jQuery Deferreds & Promises Eli Perelman @eliperelman

What are deferreds?

Provide a system to register callbacks into neatly managed queues DEFERREDS

WITHOUT DEFERREDS var  validateUser  =  function  (  username,  password,  callback  )  {          if  (  username  ===  ‘bob’  &&  password  ===  ‘123’  )  {                  callback(  ‘success’  );          }  else  {                  callback(  ‘failure’  );          }   };   validateUser(  ‘bob’,  ‘123’,  function  (  result  )  {          if  (  result  ===  ‘success’  )  {                  location  =  ‘/dashboard’;          }  else  {                  showError(  ‘Invalid  login.’  );          }   });    

WITH DEFERREDS var  validateUser  =  function  (  username,  password  )  {          var  deferred  =  $.Deferred();          if  (  username  ===  ‘bob’  &&  password  ===  ‘123’  )  {                  deferred.resolve();          }  else  {                  deferred.reject();          }          return  deferred.promise();   };   validateUser(  ‘bob’,  ‘123’  )          .done(  function  ()  {                  location  =  ‘/dashboard’;          })          .fail(  function  ()  {                  showError(  ‘Invalid  login.’  );          });    

Deferreds work with synchronous AND asynchronous functions.

Since jQuery 1.5, the $.ajax module uses deferreds.

What are promises?

Provide a common API for consuming code to register callbacks, sync or async. PROMISES

Deferreds Promises .then .then .done .done .fail .fail .always .always .reject .resolve .pipe .pipe .promise .promise .isResolved .isRejected

Coding time!