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What is state in JavaScript

Understanding State in JavaScript

One of the most significant concepts in JavaScript, especially when you start working with libraries like React, is the concept of State. But what is State? Let's dive in and decode this important concept of JavaScript.

What is State?

In JavaScript, state refers to the data stored in the application at a given moment. It's a snapshot of the condition of an application. Imagine you are playing a video game. The current level you are on, your score, and your remaining lives are all part of the game's state.

let game = {
  level: 1,
  score: 2000,
  lives: 3

The above code represents the state of a game with properties level, score, and lives.

Why is State Important?

State is crucial because it allows your application to remember information. Without state, every time you interacted with an application, it would forget what you did previously. It's like reading a book but forgetting the previous page as soon as you turn it over. Not very helpful right?

State in Functions

In JavaScript, functions can have state too. Let's consider a simple counter function:

let count = 0;

function incrementCount() {

incrementCount(); // logs 1
incrementCount(); // logs 2

Every time we call incrementCount(), our count increases. Here, the count variable is maintaining the state of our function.

Changing State

The state is not static; it changes over time based on user interaction or system events. Using our game example, state can change when a player advances a level, increases their score, or loses a life:

function advanceLevel(game) {

console.log(game.level); // logs 2

In the above code, advanceLevel function is changing the state of the game by advancing the level.

State in Libraries and Frameworks

In JavaScript libraries and frameworks like React, Vue, or Angular, state management is a key feature. They provide sophisticated methods and tools to handle state changes and updates.

For instance, in React, a component’s state is an instance of the React.Component class. It can be modified using this.setState() method.

class Game extends React.Component {
  constructor() {
    this.state = {
      level: 1,
      score: 2000,
      lives: 3

  advanceLevel = () => {
    this.setState({ level: this.state.level + 1 });

In this code, we define a state in the constructor of a React component. We then create a method advanceLevel to change the state.

State vs. Props

Props and State are both plain JavaScript objects. While both hold information that influences the output of render, they are different in one crucial aspect: props get passed to the component similar to function parameters, whereas a component's state is managed within the component, similar to variables declared within a function.


Understanding state in JavaScript is like understanding memories in a human brain. It's the mechanism by which our applications 'remember' and 'think'. Without state, our applications would be like Dory from Finding Nemo, forgetting everything the moment after it happens.

State management can sometimes get complex as applications scale, but getting a firm grasp of the basics will make things easier. Remember, a well-managed state leads to an application that behaves predictably and is easier to debug. So, keep practicing and playing around with JavaScript states, and soon it will be as familiar as the back of your hand.

Happy coding!