Props and State in React

Kelsey Dickson
3 min readDec 14, 2020


Mad props to the folks who create this awesome open-source, front-end, JS Library known as React. React is great for single-page apps, rendering Data to the DOM, routing, and state management. I find it helpful to simplify over-complicated terms and break them down, so in case you’re just starting out I hope you find these bullets helpful.


What the heck are Props?

Properties aka Props

  • Props allow us to send data through components making them dynamic and reusable
  • The values sent through propscan be strings, functions, arrays, and objects
  • Props are Read-Only
  • Props are immutable FANCY FOR unable to change
  • Can only be passed from Parent to Child.

How to use Props:

  • Define props in component’s JSX tag
  • Take in and use props in a component
App is Parent component sending props Greeting who is the Child component.

What we are doing in the App component is sending down a prop called name with the value of “Kelsey” to the Greeting component.

import React from 'react';const Greeting = (props) => {   return(
<h1>Hi {}</h1>
export default Greeting

Now the Greeting component has access to props! Inside our curly braces in JSX we have access to the value of name and can render to the screen.



What the heck is State?

  • Is a POJO (Plain Ole JavaScript Object)
  • The state object can contain as many properties as you like
  • state holds the initial information
  • Once the statechanges the component re-renders
  • If you update state, you should not modify directly, but instead, use setState()

Where does State live?

State can live in both class and functional components. However, if you choose to use a functional component, you will need to use React’s Hooks.

Here is an example of a functional component using hooks:

The output from code above:

Now, this is a class component using state:

As you can immediately see, code with hooks is much shorter syntax. Both options allow you to manage your state locally but cannot be accessed or modified outside of the component unless passing as props. While state increases complexity, it is good practice to have fewer stateful components, allowing for easier statemanagement.

Props vs State

While props and state have their differences, they do share some commonalities.

  • Both are POJO’s (Plain Ole JavaScript Objects)
  • Both trigger a render update
  • Both can contain default values

The difference between state and props:


Props and state are both important fundamental concepts in React. In my opinion, React is a wonderful library filled with magic for the developer to implement and the User to experience. If at first, it seems overwhelming and hard, just know, it does get better. Practice makes perfect!