ES2018

List of New Features

• Rest/Spread Properties
• Asynchronous iteration
• Promise.prototype.finally()
• Regular Expression improvements
  • RegExp lookbehind assertions: match a string depending on what precedes it
  • Unicode property escapes \p{…} and \P{…}
  • Named capturing groups
  • The s flag for regular expressions

Rest/Spread Properties

ES6 introduced the concept of a rest element when working with array destructuring:

const numbers = [1, 2, 3, 4, 5]
[first, second, ...others] = numbers
and spread elements:

const numbers = [1, 2, 3, 4, 5]
const sum = (a, b, c, d, e) => a + b + c + d + e
const sumOfNumbers = sum(...numbers)

ES2018 introduces the same but for objects.

Rest properties:

const { first, second, ...others } = { first: 1, second: 2, third: 3, fourth: 4, fifth: 5 }

first // 1
second // 2
others // { third: 3, fourth: 4, fifth: 5 }

Spread properties allow to create a new object by combining the properties of the object passed after the spread operator:

const items = { first, second, ...others }
items //{ first: 1, second: 2, third: 3, fourth: 4, fifth: 5 }