JavaScript Basics

JavaScript Cheat Sheet — Basic ES6 Syntax and Methods

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JavaScript is one of the most popular programming languages for web programming.

In this article, we’ll look at the basic syntax of modern JavaScript.

Arrow function

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

sum(1, 2) returns 3.

Default parameters

function print(a = 5) {

print() logs 5.

let scope

We can use let to declare variables:

let a = 3
if (true) {
  let a = 10

console.log should log 10.


const variables can only be assigned once when we initialize it:

const a = 11

We’ll get an error if we try to assign a again.

Multiline String

We can create multine string with backticks (`):

  This is a
  multiline string

Template Strings

We can interpolate expressions with ${} :

const name = 'james'
const message = `Hello ${name}`

Then message is 'Hello james'

String includes()

We can use the includes method to check if a string has the given substring.



returns true .

String startsWith()

The startsWith method lets us check if a string starts with a given substring:


String repeat()

We can use the repeat method to repeat a string:


returns ‘ababab’ .

Destructuring Array

We can use the destructuring syntax to assign array entries to variables.

For instance, we write:

let [a, b] = [3, 10];

Then a is 3 and b is 10.

Destructuring Object

We can assign object properties to variables with the destructuring syntax.

For example, if we have:

let obj = {
  a: 15,
  b: 20
let {
} = obj;

Then a is 15 and b is 20.

Object Property Assignement

We can assign properties to objects with the object property assignment syntax.

For instance, we write:

const a = 2
const b = 5
const obj = {

Then obj is:

{a: 2, b: 5}

Object Function Assignment

We can add methods to an object with the shorthand syntax:

const obj = {
  a: 'foo',
  b() {

Then we can call obj.b() to log 'b' .

Spread Operator

The spread operator lets us combine arrays into one.

For instance, we write:

const a = [1, 2]
const b = [3, 4]
const c = [...a, ...b]

And c is [1, 2, 3, 4] .


The Object.assign method lets us combine multiple objects into one.

For instance, we write:

const obj1 = {
  a: 1
const obj2 = {
  b: 2
const obj3 = Object.assign({}, obj1, obj2)

Then obj3 is { a: 1, b: 2 } .


We can get the object’s key-value pairs into an array with the Object.entries() method.

For instance, we write:

const obj = {
  frstName: 'james',
  lastName: 'smith',
  age: 22,
  country: 'uk',
const entries = Object.entries(obj);

Then Object.entries returns:



JavaScript comes with useful syntax and methods in the standard library we can use.

By John Au-Yeung

Web developer specializing in React, Vue, and front end development.

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