Chaining Promises and Promise handlers

Much of the purpose of promises is to allow the developer to serialize and reason about independent asynchronous actions. This can be accomplished by utilizing the Promise chaining feature.

Note

The code, links, and a live example of this are available at http://ngcookbook.herokuapp.com/6828/ .

How to do it...

The promise handler definition method then() returns another promise, which can have further handlers defined upon it—in a handler called chain:

var successHandler = () => { console.log('called'); }; 
 
var p = new Promise((resolve, reject) => { resolve(); }) 
  .then(successHandler) 
  .then(successHandler) 
  .then(successHandler); 
 
// called 
// called 
// called 

Chained handlers' data handoff

Chained handlers can pass data to their subsequent handlers in the following manner:

var successHandler = (val) => {  
  console.log(val);  
  return val+1; 
}; 
 
var p...