JavaScript Basics You Must Understand Before Starting with React

React becomes much easier when you understand key JavaScript concepts. This guide covers the essential JS topics every beginner should learn before starting React.

✅ Introduction

Before learning React, it's very important to understand the fundamentals of JavaScript. React is built on JavaScript, and almost everything inside React—components, props, state, and hooks—uses JavaScript concepts. If you know the core JS basics, React will feel simple and enjoyable instead of confusing.

🟦 1. Variables (let & const)

Modern JavaScript uses let and const.

• let → value can change

• const → value cannot change

React uses const a lot when defining components:

const App = () => {
  return <h1>Hello</h1>;
};

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🟦 2. Functions (especially arrow functions)

React components are functions, so you must understand:

function greet() { ... }
const greet = () => { ... }

React component example:

const Header = () => <h1>React Header</h1>;

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🟦 3. Arrays & Objects

You use arrays for lists and objects for props/state.

Array:

const items = ["React", "JS"];

Object:

const user = { name: "Sandip", age: 22 };

React example (render list):

items.map(item => <li key={item}>{item}</li>);

Note: When you use .map() in React to create a list, you must add a unique key prop, just like in the example. This is essential for React's performance!

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🟦 4. Array Methods (map is MUST)

You will use .map() in React every day.

Example:

numbers.map(n => <p>{n}</p>);

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🟦 5. Conditional Logic (if, else, ternary)

Used for showing or hiding elements.

Example:

{loggedIn ? <Home /> : <Login />}

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🟦 6. ES6 Features

These features appear constantly in React:

✔ Destructuring

const { name } = user;

✔ Spread operator

const newArr = [...oldArr, 4];

✔ Import/Export

import App from "./App";
export default App;

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🟦 7. Basics of the DOM (just the idea)

You should know:

• What is DOM

• document.getElementById

• How JS updates UI

React replaces DOM work, but knowing the concept helps.

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🟦 8. Events

Basic understanding of events is helpful:

button.addEventListener("click", ...)

In React:

<button onClick={handleClick}>Click</button>

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✅ Conclusion

If you understand these basics, learning React becomes much smoother. You don’t need to master everything deeply — just the core idea of how JavaScript works. Once your JS foundations are solid, React concepts like components, props, state, and hooks will make much more sense.

Thanks for reading! Now you know the essential JavaScript basics needed before starting React. In the next part of this React Learning Series, we’ll learn about the DOM and how React uses it. Stay tuned! 🚀

Originally published on Medium.