JuanMa juanmaguitar

Maps (ES2015)

The Map object is a simple key/value map. Any value (both objects and primitive values) may be used as either a key or a value.

> var animalSounds = new Map();
> animalSounds.set("dog", "woof");
Map {"dog" => "woof"}
> animalSounds.set("cat", "meow");

Iterators (ES-2015)

Iterators

An object is an iterator when it knows how to access items from a collection one at a time, while keeping track of its current position within that sequence.

In JavaScript an iterator is an object that provides a next() method which returns the next item in the sequence. This method returns an object with two properties: done and `value.

Symbols (ES2015 Notes)

The symbol is a new primitive type, a unique token that is guaranteed never to clash with another symbol → a kind of UUID (Universally Unique Identifier)

ES2015 symbols are values, but they’re not strings. They’re not objects. They’re something new: a seventh type of value.

The primary reason for the introduction of symbols seems to have been to facilitate adding new functionality to the language without breaking existing code (hidden and unique properties)

Con los symbol podemos añadir propiedades ocultas y unicas a los objetos que nos permiten extender objetos facilmente.

	# Generators - ES2015

	http://riadbenguella.com/how-es6-generators-are-changing-how-we-write-javascript/

	Generators are special functions that can be run, paused and resumed at different stages of their execution, thanks to the special keyword `yield`.

	```javascript
	function* myGenerator() {
	yield 'first';
	let input = yield 'second';

	// https://medium.com/@rdsubhas/es6-from-callbacks-to-promises-to-generators-87f1c0cd8f2e#.q7boouq4o

	/* Step 1: Callback hell — N levels deep */

	var request = require('request');
	var url1='http://httpbin.org/', url2=url1, url3=url1, url4=url1;

	function foo(finalCallback) {
	request.get(url1, function(err1, res1) {
	if (err1) { return finalCallback(err1); }

	/* ------------------------------------------------------- */
	/* GENERATORS USING PREV VALUES */
	/* ------------------------------------------------------- */

	function *foo(x) {
	var y = 2 * (yield (x + 1));
	var z = yield (y / 3);
	return (x + y + z);
	}

	function *fibonacci() {
	let [prev, current] = [0, 1];
	while(true) {
	[prev, current] = [current, prev + current];
	yield current;
	}
	}

	let seq = fibonacci();

	let fibonacci = {
	[Symbol.iterator]() {
	let pre = 0, cur = 1
	return {
	next () {
	[ pre, cur ] = [ cur, pre + cur ]
	return { done: false, value: cur }
	}
	}
	},

	function guidMaker(){

	function generator() {
	const S4 = () => (((1+Math.random())*0x10000)\|0).toString(16).substring(1);
	return (S4()+S4()+"-"+S4()+"-"+S4()+"-"+S4()+"-"+S4()+S4()+S4());
	}

	const done = false;
	let generated = 0;