Promise-based web architecture

To have a better understanding of the differences between Promises and traditional callbacks, consider an asynchronous task like this:

function process(callback) { 
  stepOne((error, resultOne) => { 
    if (error) { 
      callback(error); 
       return; 
      } 
 
  stepTwo(resultOne, (error, resultTwo) => { 
    if (error) { 
      callback(error); 
        return; 
    } 
 
    callback(undefined, resultTwo + 1); 
    }); 
  }); 
} 
 

If we write preceding above in Promise style, it would be as follows:

function process() { 
  return stepOne() 
    .then(result => stepTwo(result)) 
    
.then(result => result + 1); 
}

As in the preceding example, Promise makes it easy and natural to write asynchronous operations with a flat chain instead of nested callbacks. But the most exciting thing about Promise might be the benefits it...