learnES6 created by alexspark - https://repl.it/@alexspark/learnES6

learnES6.js

// constants
const NAME = `Alex Park`
console.log(`const: ${NAME}`)

// block scope: var vs let
// best explanation so far:
// https://www.sitepoint.com/joys-block-scoping-es6/
for (var i=0; i<3; i++) {
  var j = i * i
}
console.log(`hoisted var j: ${j}`)

let inf = Infinity
for (var i=0;i<3;i++) {
  let inf = i * i
}
console.log(`unhoisted let inf: ${inf}`);

let callbacks = [];
for (var i=0;i<3;i++) {
  callbacks[i] = function () { return i * 2 }
}
console.log(`
callbacks[] invoked when using var i...
callbacks[0] = ${callbacks[0]()}
callbacks[1] = ${callbacks[1]()}
callbacks[2] = ${callbacks[2]()}
`);

callbacks = []
for (let i=0;i<3;i++) {
  callbacks[i] = function () { return i * 2 }
}
console.log(`
callbacks[] invoked when using let i...
callbacks[0] = ${callbacks[0]()}
callbacks[1] = ${callbacks[1]()}
callbacks[2] = ${callbacks[2]()}
`);

// lexical scope with blocks!
{
  function fn() { return 1 }
  console.log(`fn() === 1: ${fn() === 1}`)
  
  {
    function fn() { return 2 }
    console.log(`fn() === 2: ${fn() === 2}`)
  }
  
  console.log(`fn() === 1: ${fn() === 1}`)
}

let m = [0, 1, 2, 3, 4, 5].map(i => i * 2);
console.log(`m: ${m}`);
m = [0, 1, 2, 3, 4, 5].map((i) => ({ number: i, next: i+1 }));
console.log(Object.values(m));

let context = {
  replyTo: '[email protected]',
  friends: ['anna', 'louise'],
  broadcast() {
    this.friends.forEach(f => {
      console.log(`${this.replyTo}: ${f}`)
    })
  }
}

console.log(context.broadcast());

function square() {
  const example = () => {
    let numbers = []
    for (number of arguments) {
      numbers.push(number * number)
    }
    
    return numbers;
  }
  
  return example()
}

console.log(`
lexical \`arguments\`:
  ${square(1, 2, 4, 9)}
`);

const power2defaulted = (x=1) => Math.pow(2, x);
console.log(`
  power2defaulted(): ${power2defaulted()}
  power2defaulted(2): ${power2defaulted(2)}
`);

const restAdd50 = (...r) => {
  return r.reduce((r, acc) => r + acc, 50)
};

console.log(`
  restAdd50(10, 20, 30) => ${restAdd50(10, 20, 30)}
`);

const firstShallBeLast = arr => [arr[arr.length-1], ...arr.slice(0, arr.length-1)];
console.log(`
  firstShallBeLast([1, 2, 3]) => [${firstShallBeLast([1, 2, 3])}]
`);

const asChars = word => [...word];
console.log(`
  asChars("alex"): ${asChars("alex")}
`);

const shorthandVar = 29;
const shortObj = { shorthandVar };
console.log(`
  shorthandVar: 29
  shortObj = { shorthandVar };
  shortObj.shorthandVar => ${shortObj.shorthandVar}
`);

const methodProps = {
  meth1(a, b) { return a * b },
  meth2(a, b) { return a - b }
};
console.log(`
  methodProps.meth1(2, 3) => ${methodProps.meth1(2, 3)}
  methodProps.meth2(2, 3) => ${methodProps.meth2(2, 3)}
`);

const destructList = [...'alex'];
let [first, , ,last] = destructList;
console.log(`
  const destructList = [...'alex'];
  let [first, , , last] = destructList;
  first => ${first}
  last => ${last}
`)
//[last, first] = [first, last];
//console.log(`
//  [last, first] = [ first, last ];
//  first => ${first}
//  last => ${last}
//`)

const makeComputed = (name) => ({
  name,
  ['print' + name]: function() {
    return [...name].reverse().join('');
  }
});

console.log(`
  const makeComputed = (name) => ({
    ['print' + name]: function() {
      return [...name].reverse().join('');
    }
  });
  makeComputed('Alex').printAlex() => ${makeComputed('Alex').printAlex()}
`);

let { name } = makeComputed('eunice');
console.log(`
  let { name } = makeComputed('eunice'); => ${name}
`);

class Cat {
  constructor (name, breed, owner) {
    this._name = name;
    this.owner = owner;
    this.breed = breed;
    this.meowCount = 1;
  }
  hi() {
    return `what do you want, ${this.owner}!? ehhh!?`
  }
  get name() { return this._name; }
  set name(n) { this._name = n; }
  static m () { return 'MEOWMEOWMEOW!!!!'; }
}

const cat = new Cat('Bella', 'egyptian cat', 'alex');
console.log(`
  const cat = new Cat('Bella', 'egyptian cat', 'alex');
  cat.hi() => ${cat.hi()}
`);

cat.name = 'eunice';
console.log(`
  cat.name = 'eunice'
  cat.name => ${cat.name}
  Cat.m() => ${Cat.m()}
`);