All the JavaScript You Need Before React.js

I’ve seen this happen too many times.

A developer jumps straight into React.

They learn useState, useEffect, maybe even build a few projects.

But when something breaks…

They’re stuck.

Not because React is hard.

But because their JavaScript foundation is weak.

And here’s the truth no one tells you:

React is just JavaScript.
If your JavaScript is strong, React feels easy.
If it’s weak, React feels confusing.

So before you dive deeper into React, here’s the JavaScript you actually need to master.

1. Variables, Scope & Closures (This One Changes Everything)

You already know let, const, and var.

But do you really understand scope?

Example:

function outer() {
  let count = 0

  return function inner() {
    count++
    return count
  }
}

const counter = outer()

console.log(counter()) // 1
console.log(counter()) // 2

This is a closure.