ECMAScript is a general-purpose programming language, standardized by Ecma International according to the document ECMA-262. It is a JavaScript standard meant to ensure the interoperability of web pages across different web browsers. ECMAScript 2015 was the second major revision to JavaScript that is known as ES6 and ECMAScript 6 now.
JavaScript ES6 has come-up with new syntax and awesome features to make your code more readable and modern. This language allows you to do more with less code. ES6 introduces us to many great features like arrow functions, template strings, class destruction, Modules… and more. Let’s take a look.
Arrow function
const sum = (a, b) => a + b console.log(sum(2, 6)) // prints 8
Default parameters
function print(a = 5) { console.log(a) } print() // prints 5 print(22) // prints 22
let scope
let a = 3 if (true) { let a = 5 console.log(a) // prints 5 } console.log(a) // prints 3
const
// can be assigned only once: const a = 55 a = 44 // throws an error
Multiline string
console.log(` This is a multiline string `)
Template strings
const name = 'Leon' const message = `Hello ${name}` console.log(message) // prints "Hello Leon"
String includes()
console.log('apple'.includes('pl')) // prints true console.log('apple'.includes('tt')) // prints false
String startsWith()
console.log('apple'.startsWith('ap')) // prints true console.log('apple'.startsWith('bb')) // prints false
String repeat()
console.log('ab'.repeat(3)) // prints "ababab"
Destructuring array
let [a, b] = [3, 7]; console.log(a); // 3 console.log(b); // 7
Destructuring object
let obj = { a: 55, b: 44 }; let { a, b } = obj; console.log(a); // 55 console.log(b); // 44
object property assignment
const a = 2 const b = 5 const obj = { a, b } // Before es6: // obj = { a: a, b: b } console.log(obj) // prints { a: 2, b: 5 }
object function assignement
const obj = { a: 5, b() { console.log('b') } } obj.b() // prints "b"
spread operator
const a = [ 1, 2 ] const b = [ 3, 4 ] const c = [ ...a, ...b ] console.log(c) // [1, 2, 3, 4]
Object.assign()
const obj1 = { a: 1 } const obj2 = { b: 2 } const obj3 = Object.assign({}, obj1, obj2) console.log(obj3) // { a: 1, b: 2 }
Object.entries()
const obj = { firstName: 'Vipul', lastName: 'Rawat', age: 22, country: 'India', }; const entries = Object.entries(obj); /* returns an array of [key, value] pairs of the object passed */ console.log(entries); /* prints [ ['firstName', 'Vipul'], ['lastName', 'Rawat'], ['age', 22], ['country', 'India'] ]; */
spread operator
const a = { firstName: "Barry", lastName: "Manilow", } const b = { ...a, lastName: "White", canSing: true, } console.log(a) // {firstName: "Barry", lastName: "Manilow"} console.log(b) // {firstName: "Barry", lastName: "White", canSing: true} // great for modifying objects without side effects/affecting the original
Destructuring Nested Objects
const Person = { name: "John Snow", age: 29, sex: "male", materialStatus: "single", address: { country: "Westeros", state: "The Crownlands", city: "Kings Landing", pinCode: "500014", }, }; const { address : { state, pinCode }, name } = Person; console.log(name, state, pinCode) // John Snow The Crownlands 500014 console.log(city) // ReferenceError
Exponent operator
const byte = 2 ** 8 // Same as: Math.pow(2, 8)
Promises with finally
promise .then((result) => { ··· }) .catch((error) => { ··· }) .finally(() => { // logic independent of success/error }) // The handler is called when the promise is fulfilled or rejected.
