JS ES6: Iterable | Iterators. Play in repl: http://bit.ly/1GvjFg7

index.js

/*
  Iterators | Iterables:
  
  Iterable (data structure):             Iterator (obj that enumirates data):
  [Symbol.iterator]()          --->      .next()

  `for of` interate only on Iterables
*/

// array
for (let a of [1, ...[2, 3, 4], 'foo']) {
  console.log(a);
}
console.log();

// string
for (let x of '\u2744\u274E') {
    console.log(x);
}
console.log();

// Map: [key, value] pair + destructuring
let map = new Map().set('foo', 1).set('bar', [1, 2, 3]);
for (let [k, v] of map) {
  console.log(`key = ${k}, value = ${v}`)
}
console.log();

// Set: sequance
let set = new Set().add('foo').add(123);
for (let s of set) {
  console.log(s)
}
console.log();

// arguments...

// DOM
for (let node of document.querySelectorAll('a')) {
  console.log(node)
}

/*
  TASK: create function take(n, iterable),
        which returns an iterable over
        the first n items of iterable.
*/      
function take (n, iterable) {
  // do
}

let arr = ['a', 'b', 'c', 'd'];
for (let x of take(2, arr)) {
    console.log(x);
}
// Output:
// a
// b