Props in React.js: A Beginner’s Guide

Props, short for properties, in React.js are how components talk to each other. They let you make components that are reusable, testable, and isolated. If state makes your application ‘live’ and ‘react’ to user inputs, props let your components ‘communicate’ and ‘cooperate’.

This guide will give you a comprehensive understanding of how props work in React.

What are Props?

Props are to a React component what arguments are to a function. They are passed from a parent component to a child component and become properties of the child component. Here’s an example:

function Greeting(props) {
  return <h1>Hello, {props.name}</h1>;
}

In the Greeting component, props is an object with a property name. When we use the Greeting component, we can pass a name prop to it:

<Greeting name="John Doe" />

Props are Read-Only

In React, props are read-only. This means that a child component cannot modify the props it receives. This enforces the idea of ‘one-way data flow’ or ‘top-down data flow’ in a React application. Here’s an example:

function Greeting(props) {
  props.name = 'John Doe'; // This will result in an error
  return <h1>Hello, {props.name}</h1>;
}

Passing Multiple Props

You can pass multiple props to a component:

<Person name="John Doe" age={30} />

Inside the Person component, you can access these props like so:

function Person(props) {
  return <h1>Hello, {props.name}. You are {props.age} years old.</h1>;
}

Passing Functions as Props

React allows you to pass functions as props, enabling child components to communicate with their parents:

function ParentComponent() {
  function showAlert() {
    alert('Button clicked!');
  }

  return <ChildComponent onClick={showAlert} />;
}

function ChildComponent(props) {
  return <button onClick={props.onClick}>Click me</button>;
}

In the above example, the ParentComponent passes a function showAlert as a prop to ChildComponent. ChildComponent can then call this function when its button is clicked.

Conclusion

Understanding props is fundamental to building interactive and dynamic applications in React.js. They facilitate the flow of data and functions between components, enabling you to build complex applications with simpler, reusable parts.

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