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ES6 Bullet points

Class

  1. Classes are just syntactic sugar.
  2. Instantiating an es6 class has same syntax as of prototypal way
  3. constructor() is automatically called on creating instance of the class.
  4. extends keyword is used to inherit from class
  5. super() call returns the execution of same function from parent
	class LogView extends View {
	  render() {
		var compiled = super();
		console.log(compiled);
	  }
	}

Promise

  • A promise can only succeed or fail once. It cannot succeed or fail twice, neither can it switch from success to failure or vice-versa
  • If a promise has succeeded or failed and you later add a success/failure callback, the correct callback will be called, even though the event took place earlier

State of Promise:

The core idea behind promises is that a promise represents the result of an asynchronous operation. A promise is in one of three different states:

  • Pending - The initial state of a promise.
  • Fulfilled - The state of a promise representing a successful operation.
  • Rejected - The state of a promise representing a failed operation.

Fate of Promise:

Promises have two possible mutually exclusive fates: resolved, and unresolved.

  • A promise is resolved if trying to resolve or reject it has no effect, i.e. the promise has been "locked in" to either follow another promise, or has been fulfilled or rejected.
  • A promise is unresolved if it is not resolved, i.e. if trying to resolve or reject it will have an impact on the promise.

A promise can be "resolved to" either a promise or thenable, in which case it will store the promise or thenable for later unwrapping; or it can be resolved to a non-promise value, in which case it is fulfilled with that value.

A promise whose fate is unresolved is necessarily pending.

###Promise API Reference###

Static Methods

Promise.resolve(promise);
Returns promise (only if promise.constructor == Promise)

Promise.resolve(thenable);
Make a new promise from the thenable. A thenable is promise-like in as far as it has a "then" method.

Promise.resolve(obj); Make a promise that fulfills to obj. in this situation.

Promise.reject(obj);
Make a promise that rejects to obj. For consistency and debugging (e.g. stack traces), obj should be an instanceof Error.

Promise.all(array);
Make a promise that fulfills when every item in the array fulfills, and rejects if (and when) any item rejects. Each array item is passed to Promise.resolve, so the array can be a mixture of promise-like objects and other objects. The fulfillment value is an array (in order) of fulfillment values. The rejection value is the first rejection value.

Promise.race(array);
Make a Promise that fulfills as soon as any item fulfills, or rejects as soon as any item rejects, whichever happens first.

Constructor:
new Promise(function(resolve, reject) {});
Note: Any errors thrown in the constructor callback will be implicitly passed to reject().

Instance Methods

promise.then(onFulfilled, onRejected)
onFulfilled is called when/if "promise" resolves. onRejected is called when/if "promise" rejects. Both are optional, if either/both are omitted the next onFulfilled/onRejected in the chain is called. Both callbacks have a single parameter, the fulfillment value or rejection reason. "then" returns a new promise equivalent to the value you return from onFulfilled/onRejected after being passed through Promise.resolve. If an error is thrown in the callback, the returned promise rejects with that error.

promise.catch(onRejected)
Sugar for promise.then(undefined, onRejected)

References:
Specification: https://promisesaplus.com/
Polyfill: https://github.com/jakearchibald/ES6-Promises#readme
MDN: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise