JavaScript ES6 Cheat sheet

About JavaScript ES6

JavaScript ES6 (also known as ECMAScript 2015 or ECMAScript 6) is the newer version of JavaScript that was introduced in 2015. ECMAScript is the standard that the JavaScript programming language uses. ECMAScript provides the specification on how JavaScript programming language should work.

JavaScript ES6 cheat sheets are:

Arrow function:

const sum = (a, b) => a + b 

console.log(sum(2, 6)) // prints 8

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 assignment:

const obj = {

a: 5,

b() { 

console.log('b')

  }

}

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

Object.assing():

const obj1 = { a: 1 }

const obj2 = { b: 2 }

const obj = object.assing( {} ,

       obj1, obj2)

console.log(obj3)

// { a: 1, b: 2 }

Object.entries():

const obj = {

 firstname: 'firstname' ,

 lastname: 'lastname' ,

 age: 24,

 country: 'India',

};

const entries = object.entries(obj);

/* returns an array of [key, value]

 pairs of the object passed */

console.log(entries);

/* prints

[

['firstname', 'FirstName'],

['lastname', 'LastName'],

['age', 24],

['country', 'India'] 

]; */

Const:

// can be assigned only once

const a = 55

a = 44 // throws an error

Promises with family:

promise

 .then((result) => { . . .})

 .catch((error) => {. . .})

 .finally(() => { /* logic

independent of success/error */ })

/* The handler is called when the 

promise is fulfilled or rejected.*/

Multiline string:

console.log(`

 This is a

 multiline string

`)

Template strings:

const name = 'world'

const message = `Hello ${name}`

console.log(message)

// prints "Hello World"

Spread operator:

const a = {

  firstname: "FirstName",

  lastname: "LastName",

}

const b = {

 . . . a,

lastname: "LastName2",

canSing: true,

}

console.log(a)

//{firstname: "FirstName , lastname: "LastName1"}

console.log(b)

/* {firstname: "FirstName , lastname: "LastName2",

canSing = true} */

*/ great for modifying objects without side

effects/affecting the original */

Exponent operator:

const byte = 2 ** 8

// same as: Math.pow(2, 8)

Spread operator:

const a = [ 1, 2 ]

const b = [ 3, 4]

const c = [ . . . a, . . . b ]

console.log(c) // [1, 2, 3, 4]

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

Destructuring nested objects:

const Person = {

name: "Harry Potter",

age: 29,

sex: "male",

materialStatus: "single",

address : {

country: "USA"

state: "Nevada",

city: "Carson City",

pinCode: "500014",

},

};

const { address : { state, pincode }, name } - Person;

console.log(name, state, pinCode)

// Harry Potter Nevada 500014

console.log(city) // ReferenceError