ES6 or ES2015

Block scoping

let is the new var.

// Block scoping (let)
function fn () {
  let x = 0;
  if (true) {
    let x = 1; // only inside this `if`
  }
}
// Constants
const a = 1;

Promises

• For asynchronous programming.

new Promise(fn)
  .then(fn)
  .catch(fn)
Promise.all(/*...*/)
Promise.race(/*...*/)
Promise.reject(/*...*/)
Promise.resolve(/*...*/)

References:

• http://ricostacruz.com/cheatsheets/es6.html
• https://babeljs.io/docs/learn-es2015/
• https://ponyfoo.com/articles/es6