Fidelity

A simple promises-aplus implementation. I wrote this over the course of a few days with some simple goals in mind.

• Gain a better understanding of how Promises work
• Pass all of the tests in the Promises/A+ Compliance Test Suite
• Experiment with some of Douglas Crockford's object creation ideas
  • eliminate use of the this keyword
  • eliminate use of the new keyword

Installing

npm install fidelity

Usage

A fidelity promise takes a function as an argument. This function accepts a resolve and a reject object. Suppose we have a function f() that takes some time to complete asynchronously. We can call this function using a promise.

var promise = require('promise');

var p = promise(function(resolve, reject) {
  var result = f();
  if (result) {
    resolve(f);
  } else {
    reject('Some error occurred');
  }
})

The object returned from a call to promise() has a function, then(). This function takes two arguments, each a function. The first is called with the return value (if any) of the promise function if it is successfully fulfilled. The second function is called in the event of an error.

p.then(function(result) {
  console.log('sucessful result ', result);
}, function(err) {
  console.log('whoops!', err);
});

Testing

To run the full suite of the Promises/A+ spec, run npm test from the command line.