9 JavaScript Topics You Must Know Before Learning React in 2024

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You can't learn React properly without a solid foundation in JavaScript. Here are the 9 essential topics you absolutely need to know, based on years of teaching experience. For a comprehensive primer, you might find our JavaScript 101: Everything Beginners Need to Know in One Video helpful.

1. Variables & Scope

Understand how to declare and use variables:

let, block-scoped, can be reassigned
const, block-scoped, cannot be reassigned (but mutable for objects/arrays)
var, function-scoped, avoid in modern code
Know hoisting and scope rules

2. Functions, The Heart of JavaScript

Functions are central to React. Master these:

Arrow functions: shorter syntax, lexical this binding
Higher-order functions: functions that take or return other functions
Callback functions

3. Arrays & Objects (ES6 Features)

React apps revolve around data, you must handle objects and arrays fluently:

Object destructuring: extract properties with { name, age } = obj
Array destructuring: [first, second] = arr
Spread operator (...): clone/merge arrays/objects
Rest operator (...): gather remaining elements into an array

4. Conditionals & Logical Operators

Used constantly for rendering logic in React:

if / else statements
Ternary operator: condition ? valueIfTrue : valueIfFalse
Logical AND (&&) and OR (||) for conditional rendering
Optional chaining (?.): safely access nested properties

5. Array Methods: map, filter, reduce, sort

These functional methods are non-negotiable for React. Our Complete JavaScript Beginner Course: Projects, Fundamentals, and API Integration covers these methods extensively:

| Method | Purpose | |--------|---------| | map() | Transform every element in an array (most used in React) | | filter() | Create a subset of elements | | reduce() | Accumulate values into a single result | | sort() | Order array elements |

You will write map() in virtually every React component.

6. Event Listeners & Timers

User interactions are the soul of web apps:

Click, mouse, keyboard events (e.g., click, mouseup, keydown)
Event bubbling vs event capturing, understand propagation
setTimeout() and setInterval() for delayed/periodic actions

7. Callbacks & Promises

Making API calls requires understanding asynchronous code:

Callbacks: basic async pattern (watch out for callback hell)
Promises: the modern way to handle async operations
Promise APIs: Promise.all(), Promise.race(), etc.
fetch() function, the foundation for network requests

8. Async / Await

A cleaner, more readable syntax on top of promises:

async function getData() {
  const response = await fetch(url);
  const data = await response.json();
  return data;
}

Used extensively in modern production React code
Makes async code look synchronous and easy to debug

9. Error Handling: try / catch

Always expect and handle errors gracefully:

Wrap async code and API calls in try {} catch (error) {}
Prevents app crashes and gives you control over failures
Essential for production-ready applications

Final Advice

Before starting React, ensure you are comfortable with all nine topics above. If you know most of them, you're ready to begin your React journey. Focus on understanding the concepts deeply, not just syntax, because React will demand it. When you're ready to move forward, our Maîtrisez React : JSX, ReactDOM et création de composants guide will help you get started.

Good luck, and happy coding!

before you start learning reactjs you should definitely know JavaScript you know it has been 7 years since I'm

coding in react and it has been three years since I actively teaching react to students right I have taught a lot of

students and I have observed that uh a lot of students need to know basics of HTML CSS and JavaScript before they can

move and start learning react okay so in this video I will be covering all the topics that you should know inside

JavaScript before you start learning react if you will cover these topics it will

your react Learning Journey will become very smooth and it will be very helpful for you and this is the right path to

learn and master reactjs and become a great front-end developer in 2024 so basically before you learn react you

should definitely know basics of HTML and CSS because HTML and CSS is the backbone of all the websites that you

make right any web app will you make HTML and CSS are the main things that will be rendered onto the Dom the major

thing is Javascript right and the major doubt from the students that I get is how much JavaScript should I know right

so this video is primarily focusing upon these JavaScript topics that you should know before you can start learning

reactjs now let me just cover these topics one by one and I will tell you how much should you learn inside these

topics also as I go ahead in this video I'll start from the basics and we'll tell you the advanced topics also which

you should know as a uh good react developer so the first topic over here is you should know the basics of

JavaScript that is how variables work right what is a let variable what is a const variable what is a where variable

right how do you define these variables how these variables are HED how variables work right uh you should know

this Basics right and uh you know if you want to learn this you can just go ahead and watch out Namaste JavaScript I have

covered all of this the second thing is you should know about functions right functions is the heart of JavaScript

functions is is the beautiful thing the best thing about JavaScript is functions everything whatever happens inside

JavaScript happens actually inside a function right so you can't learn JavaScript without learning functions

and functions are the core part of react as well now inside functions you have to note that you should know Arrow

functions right know what is Arrow functions know the syntax of it you should be able to write it the second

thing you should know what are higher order functions right just check what are higher order functions so if you

want to learn both of them I have also covered these in my free playlist Namaste JavaScript on YouTube just go

ahead and check it out in my YouTube channel now the third thing is arrays and objects right so a lot of things

that we will do while building an web app it is about arrays and objects you cannot avoid arrays and objects if you

are working with react or any web applications right so you should know how to do with arrays and objects right

you should know when I say arrays on objects you should know how d structuring works right it is an es6

concept note it Down Right destructuring object destructuring array destructuring rest operator spread operator right

these four things right you have to be aware of right you should be able to deal with arrays so these are the four

things you should know let me repeat it down object destructuring array destructuring rest operator spread

operator these four things you should know you cannot do anything if you don't know how to deal with Arizon objects in

JavaScript the fourth thing you should know is if else and conditions right so basically how do you write if and else

cases in uh JavaScript and then basically tary operator and the uh conditional rendering right basically

the and and operator right so basically it is very important and we use inside react when we build our projects right

when I was teaching Namaste react I used a lot of conditional rendering a lot of people get confused with the syntax when

they see a question mark and a dot dot right so you should know tary operator and then uh and and symbol that is the

and operator right uh very important and the or operator along with these three things you should also know optional

chaining in JavaScript right now the fifth thing you should know is map filter and reduce function along with a

sort function so basically see when you are dealing with arrays and objects so a map function a filter or reduce a sort

function is very much right these are the functions which are given by JavaScript for array operations right

you cannot avoid it and you know trust me whenever you are writing react map function you should you should be able

to write it very fluently right the maap function in JavaScript uh I have a video on my Channel about map filter and

reduce go and watch it up right before you start learning react because that will help you a lot in your react

Journey the sixth thing that you should know is event listeners right so learn about event listeners when I say event

listeners that means click event on Mouse up event on key down event and all these events right how does event work

when you click on it how does that event work right you know there are two concepts event bubbling and capturing

right so I have made these videos on my YouTube channel right go ahead search for event bubbling on YouTube right and

check out my video right that would be very helpful for you before you start learning reactjs because events are the

core part of any web application right you have to write buttons and you have to click them so you would definitely

need events so you should know events along with events you should also know how set time out works right set timeout

set interval because there are a lot of features that you would build in your application that would need these kind

of functionalities and you should know these and all these things are covered in Namaste JavaScript again so you can

go ahead and check it out over there on my channel and you know I am not promoting my videos or Namaste

JavaScript over here it is just that see everything is available for free on YouTube learn it from that playlist or

learn it from outside the internet but I am just honestly telling you that you would need this if you want to become a

react developer the seventh thing that you should know is call backs promises very much right so what is call

backs right I started Namaste JavaScript season 2 I covered call back call back hell promises promise functions cover

all of this right without promises you cannot make API calls right you should know what is a promise you should know

the in-depth promise right and then promise apis there are three videos right I think three or four videos in

which I have covered call back call back hell promises promise apis right watch those four videos in Namaste JavaScript

season 2 right uh all these episodes and it will help you to understand what is promises without promises right you you

cannot go ahead and learn react because very important whenever you'll have to make an API call and get the data you

should know promises in depth that is very very very important before you start learning reactjs and when I say

promises that means you should definitely know how fetch function Works everything right I have covered

everything in those videos go ahead and watch those videos the eighth thing that you should know is async await right I

know that Pro see async await is kind of like an alternative for promises right it's a new way of handling promises okay

it's kind of like like a sugar quoting on top of promises but it's a very good thing lot of modern react code that we

write uses async await whenever I teach react to students whenever I take examples whenever I teach in Namaste

react whenever I build projects I use asyn AIT asyn aate is a very good syntax you should definitely know asyn ofate

before you start writing production ready react code ninth topic is try catch right yes so try catch is an

important thing you should know when you are you know when you always are making an API call or writing an asyn C

function or lot of places right so it is for error handling error handling is a major concept whenever you are building

a large scale production ready web application in react right uh whenever I was teaching in Namaste react right I

used a lot of TR catch so that I can catch those errors right I can found bugs in my API calls and then I can

handle them properly okay so you should definitely know error handling if you are going to learn reactjs right so

please please please learn it before you can go ahead and do that where should you learn see I have covered a little

bit of TR catch inside my async video right async C video but but you can also go ahead and find it out more on the

internet uh I have not made a separate video on tratch but I already have covered that in ising so you can go

ahead and watch that video again so these were the nine topics important topics that that you should must know

before you start learning reactj if you know mostly all of them then you can go ahead and successfully start learning

reactjs time for a promotion right so basically I also have a reactjs course which is Namaste react I will give you

the link in the description I have a promo code which is running up right now we have special discounts running in you

can learn from there or I'm telling you that okay if you don't want to learn from my course it's okay right I am not

here to make this video just to say my course okay learn it from outside but I as a teacher want to tell you that if

you are going to learn reactjs in 2024 then definitely you should know these topics inside JavaScript you know see

wherever you learn from learn and wish you the best in your career and go ahead learn it because reactjs is the most

popular front end library right now if you are a front-end developer if you know react there's a huge demand of you

in Market okay so go ahead learn it from wherever you wish to if you want to check out my course I will give you the

link in the description I have become active on YouTube once again if you want me to cover more topics around react

around JavaScript comment down below I'm looking out for topics from you all and I will make more such amazing videos for

you all thank you for [Music] watching

What is the most important JavaScript skill I need before learning React?

Why should I avoid using `var` in modern JavaScript for React?

How do arrow functions differ from regular functions when used in React?

What are the key ES6 features I should know for handling data in React?

How do I conditionally render content in React using JavaScript?

What is the best way to handle async operations like API calls in React?

Why is understanding event propagation important for React development?

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