Key ES2015 Features

ES2015.js

function takesNamedParameters({ id, name } = {}) {
  console.log(id, name);
}
// Rest parameters
function variadic(a, b, ...theArgs) {
  return Array.isArray(theArgs); // true
}

let ary = [1, 2, 3, 4];
// Default function parameters
function takesIndividualArguments(a = 0, b = 0, c = 0, d = 0) {
  console.log(a, b, c, d);
}
// Spread operator
takesIndividualArguments(...ary);

// Object initializer
function returnsAnObject(id, name) {
  // instead of { id: id, name: name }
  return { id, name }; // from variables to object properties
}

// Object destructuring
let { name } = { id: 0, name: 'Neo' }; // from (only selected) object properties to variables

// Object.assign
function complex(options = {}) {
  let defaults = {
    // ...
  };
  let settings = Object.assign({}, defaults, options); // merge and overwrite properties from right to left
}

// Array destructuring
let [a, , b, ...rest] = [1, 2, 3, 4, 5];
console.log(a, b, rest); // 1 3 [4, 5]

for (let number of ary) {
  console.log(number);
}

// MDN: Map, Set, WeakMap and WeakSet

// Make plain objects iterable
Object.prototype[Symbol.iterator] = function () {
  let i = 0;
  let done = false;
  let keys = Object.keys(this);
  let next = () => {
    if (i >= keys.length) done = true;
    return { done, value: this[keys[i++]] };
  };

  return { next };
};

let obj = returnsAnObject(0, 'Neo');
// Ex.1 with a iterable object
for (let i of obj) {
  console.log(i);
}

// Ex.2 with a iterable object
[...obj]; // [0, 'Neo']

// Ex.3 with a iterable object
[_id, _name] = obj;
console.log(_id, _name);

// Make plain objects iterable
Object.prototype[Symbol.iterator] = function* () {
  let keys = Object.keys(this);
  for (let key of keys) {
    yield this[key];
  }
};