Callback hell be gone!

1-callback-hell.js

// An example in classic callback hell.
// In this example, talkToAPI uses a callback like we're used to

talkToAPI('login', function(err, res){
  doStuff(res);
  
  talkToAPI('getUser', function(err, res){
    doStuff(res);
    
    talkToAPI('extraData', function(err, res){
      doStuff(res);
      
      talkToAPI('saveChanges', function(err, res){
        doStuff(res);
        
        talkToAPI('reloadUser', function(err, res){
          doStuff(res);
        });
      });
    });
  });
});

2-promises-wrong.js

// Instinctively, we want to do something similar with promises.
// In this example, talkToAPI returns a Promise instead of using a callback.

talkToAPI('login')
  .then(function(res){
  
    doStuff(res);
    talkToAPI('getUser')
      .then(function(res){
      
        doStuff(res);
        talkToAPI('extraData')
          .then(function(res){
          
            doStuff(res);
            talkToAPI('saveChanges')
              .then(function(res){
              
                doStuff(res);
                talkToAPI('reloadUser')
                  .then(function(res){
                  
                    doStuff(res);
                    // As you can see, this is even worse in terms of clutter. But don't worry, it gets better.
                  
                  })
                  .catch(function(err){
                  });
              
              })
              .catch(function(err){
              });
          
          })
          .catch(function(err){
          });
      
      })
      .catch(function(err){
      });
  
  })
  .catch(function(err){
  });

3-promises-proper.js

// Now this is how we can use the beauty of promises.
// In this example, talkToAPI() returns a Promise.

talkToAPI('login')
  .then(function(res){
    doStuff(res);
    return talkToAPI('getUser'); // Return a new promise that will have to resolve before the next .then() is called
  })
  .then(function(res){
    doStuff(res);
    return talkToAPI('extraData');
  })
  .then(function(res){
    doStuff(res);
    return talkToAPI('saveChanges');
  })
  .then(function(res){
    doStuff(res);
    return talkToAPI('reloadUser');
  })
  .then(function(res){
    doStuff(res);
  })
  .catch(function(err){
  });

Wuv it!