Pre-requisites For React JS

JavaScript Fundamentals

Variables and Data Types: Understand let, const, and var, as well as primitive types (string, number, boolean, null, undefined, symbol) and objects.

Control Structures: Master if statements, switch cases, loops (for, while), and error handling with try/catch.

Functions: Know how to declare functions, use function expressions, and understand arrow functions.

Scope and Hoisting: Understand function scope, block scope, and how hoisting works.

ES6+ Features: 

Familiarize yourself with:

Template literals

Destructuring assignment

Spread and rest operators

Default parameters

Modules (import/export)

Asynchronous JavaScript: 

Understand callbacks, Promises, and async/await for handling asynchronous operations.

ES6+ Syntax:

Arrow Functions: Shorter syntax for writing functions.

Destructuring: Extracting values from arrays or objects.

Spread and Rest Operators: ... for expanding arrays/objects or collecting arguments.

Modules: import and export syntax to work with multiple JavaScript files.

Functions and Scope:

Functions: Know how to write and use functions.

Closures: Understanding how inner functions access outer function variables.

Block Scope: Understanding let, const, and var.

Objects and Arrays:

Object Literals: Creating and manipulating objects.

Array Methods: Functions like .map(), .filter(), and .reduce() are heavily used in React.

Asynchronous JavaScript:

Promises: Know how to handle asynchronous operations with .then() and .catch().

Async/Await: Writing cleaner asynchronous code.

Fetch API: Basic understanding of how to make network requests.

Event Handling:

Know how to work with events, especially in the browser (e.g., addEventListener, handling user inputs).

DOM Manipulation (optional for React but helpful):

Basic knowledge of selecting and manipulating DOM elements.