Javascript

The basics

Syntax and structure

Variables

Var

Let

Const

Block vs function scope

Data types

String

Single quote

Double quote

String interpolation

Multi-line strings

Number

Boolean

Null

Undefined

Symbol

Bigint

Objects

Operators

Basic syntax

Comments

Single-line comments (//)

Multi-line comments

A multi line comment allows you to have multiple lines commented.

/* the value of x is 1 */
const x = 1;

Functions

Function Declarations vs. Expressions

: Differences and use cases.

Arrow Functions: Syntax, this binding, and when to use them

Higher-Order Functions: Functions that take other functions as arguments or return them

Closures: How closures work and practical use cases

Default Parameters and Rest/Spread Operators: …rest, …spread, and default values

Objects

Object Literals: Creating and manipulating objects

Object Destructuring

Properties and Methods: Adding, deleting, and accessing properties

Arrays and Iteration

Array Methods: map, filter, reduce, forEach, some, every, find, findIndex, etc

Iteration: for, for…of, for…in, while, and do…while loops

Array Destructuring: Extracting values from arrays

Multidimensional Arrays: Working with nested arrays

Advanced

Type coercion

Optional chaining

Nullish coalescing

Testing: Writing unit tests with tools like Jest or Mocha

Code golfing

These tips are for code golfing specifically, and are not generally applicable to the JavaScript language.

Use short variable names

Use single-letter variable names (a, b, c, etc.) where possible.

Example:

let x = 10;

// Instead of
let count = 10;

Remove variable declaration

Often it is not required to declare a variable with const, let or var.

Example:

x = 10;

// Instead of
let x = 10;