Published in: ReactJS

What are Props in React JS? How to Use and Pass Properties to Components

Author Niraj Gohel

Published on: October 18, 2023

Introduction to React and its features

Understanding the concept of React

react js props, a renowned JavaScript library, optimizes the development of web applications. By employing a component-based architecture, it facilitates the creation of react apps, breaking down the user interface into reusable fragments. This unique approach, widely used by websites like Facebook, Twitter, and Netflix, differs significantly from other frameworks and hence, presents a learning curve for new adopters. This tutorial will guide you through the process of building and connecting these components together.

ReactJS key features

Among many, critical features of React include:

1. JSX: It’s an XML/HTML-like syntax used by React, blending HTML with JavaScript in a manner akin to a project file uploaded on Github.
2. Components: React’s encapsulation of parts of the user interface as components promotes code reusability—a similar concept to Github’s function of code hosting.
3. Unidirectional data flow: React employs a one-way data flow, enhancing readability and efficiency, further bolstered by Github’s version control capabilities.
4. Virtual DOM: This is an in-memory data structure for updating parts of the web page without a full page refresh, much like the ‘react-dom’ library’s purpose in a React project.
5. React Hooks: These functions let you use state and other React features without writing a class, akin to ‘react-dom’ in a js file of a React project.

Noteworthy, these elements, combined with Github and react-dom, make React a top choice for web developers.

Unveiling React Props

What are React JS Props?

React JS Props, standing for properties, are a key aspect of React JS. They utilize the props syntax to enable components to communicate in a uni-directional flow, primarily from child to parent components. Like HTML attributes, you can pass any JavaScript value through them, including props objects, arrays, and functions, thus showcasing their versatility. They’re read-only, prohibiting alterations within child components, thereby preserving data integrity. This syntax is equivalent to reading properties from a function parameter. Because they don’t use any of their props directly, sometimes a more concise “spread” syntax is used.

Understanding how props change over time

React Props are not always static. They can vary over time, demonstrating dynamic data outputs. That’s because they serve as a reflection of a component’s data at any given moment, not just at the start. But remember, props are immutable—a computer science term meaning “unchangeable”. To update props, or effectively utilize their data output capacities, a component must “request” its parent component to send it different props. It’s similar to how data is passed from child to parent components in Angular with the @Output decorator.

Passing and Accessing Props in React Components

Passing props to a component

To pass props to a component in React is fairly easy. Much like handling an input element in HTML, you pass arguments to a function. Wrap the prop and its value within the component’s opening tag in the parent component, similar to an HTML attribute or input element. These props can then be accessed within the child component using the prop’s name.

// Greeting.js
import React from 'react';

const Greeting = (props) => {
  return (
    <div>
      <p>{props.message}</p>
    </div>
  );
};

export default Greeting;

// App.js
import React from 'react';
import Greeting from './Greeting';

const App = () => {
  return (
    <div>
      <Greeting message="Hello, React Props!" />
    </div>
  );
};

export default App;

Accessing and using Props in React components

Accessing Props in React components depends on the component type. In the class-based components context, props can be tapped into using this.props. Alternatively, functional components utilize the method of passing props as parameters to the function, thereby allowing for direct access getElementById(‘app’). Through the implementation of getElementById, props can effectively make the elements in your components dynamic and enhance flexibility, promoting component reuse.

Deep dive into props functionality

The use of ‘this.props’ in React

In class-based components, ‘this. props’ is used to access the properties forwarded from a parent component, adopting the concept of ‘props syntax’. Similar to destructuring a function parameter, when you print console.log(this.props) in a specific component, it unveils an object containing all the props passed to that component. This technique, indeed, demonstrates key-value pair representation, forming bridges between variables from the parent to child components. Equally important it is to honor the read-only nature of ‘this.props’.

React children prop: its role and significance

The React children prop plays a special role – managing the content between the opening and closing tags of a component. This is an essential feature emphasising how React nurtures component composition using props objects. For instance,

import React from 'react';

// Parent component: DisplayUser
const DisplayUser = ({ children }) => {
  return (
    <div>
      <h1>Welcome, User!</h1>
      <div>{children}</div>
    </div>
  );
};

// App component using the DisplayUser component
const App = () => {
  return (
    <div>
      <DisplayUser>
        <p>I am a child</p>
      </DisplayUser>
    </div>
  );
};

export default App;

In this case, I am a child get channeled to DisplayUser via the children prop. With the help of props objects, the children prop empowers parent components to pass in any JavaScript value, including primitives, JSX, or even other components, into their child components. With a significant role in ReactJs, props objects are pivotal to this exchange.

Exploring State vs. Props

Differences between State and Props

• State and props are fundamental aspects of React, but have distinct differences.
• State is used within individual components to store required data for rendering to the view, whereas props are used for passing data and event handlers from parent components to children components.
• State data has the ability to change over time and is mutable, making state capable of being both readable and writable. In contrast, once set, props are immutable — they cannot be changed and are only read-only.
• State can only be used in class components, whereas props can be used in both functional and class components.
• The state represents local data that is only used and maintained by one component, while props facilitate inter-component communication.
• State data is usually updated through event handlers, on the other hand, prop data is set by the parent component for the child components.
• Props enable unidirectional or bidirectional communication, whilst the state is used for rendering dynamic data in the component.
• Also worth noting are some common pitfalls with passing props in React which could stump newcomers to the framework.

When to use State over Props and vice versa

The choice between State and Props depends on the scenario. 1.Props: Ideal for passing read-only attributes from parent to child components. Prop values don’t change within the component receiving it. Use Props when the data is coming from the parent component.

1. ReactJS States: Favour when you need to initialize and manage data that can change over time within a component. The state, which according to Caltech Coding Bootcamp is a built-in object, holds mutable data and gets updated whenever there are user interactions. Therefore, you first need to set the state within the parent component.

Summarily, utilize Props for static data and ReactJS States for dynamic data.

Advanced Props Usage: Destructuring and Default Props

Understanding destructuring props in React

Destructuring in React serves to make your code more readable and concise. It’s a JavaScript feature that extracts pieces of data from objects or arrays into standalone variables. The method of exporting separate pieces of data is a crucial aspect of JavaScript functionality, particularly in React.

In React, destructuring is achieved by grouping your properties within curly braces – either within the function body or directly as the function’s parameter.

function Product(props) {
const {img, name, desc, price} = props;
}
export default Product;

or

export default function Product({img, name, desc, price}) {}

This export statement makes the Product component available for use in other components, thereby widening its scope.

In essence, destructuring props simplifies code, enhances readability, and allows the cleanly export of components in scenarios with several properties. Here is an example showing a before and after comparison of code with and without destructuring and exporting.

Default Props: What they are and how to use them

Default Props in React are like backup values for your component properties. Just as props might remind you of HTML attributes, Default Props are comparable to these. They’re essentially props objects that kick in when no prop value or undefined is passed to a component, thanks to the way React works.

Think of it like a function argument’s default value in JavaScript. When you don’t provide a value for the argument, it falls back to its default value. This operation ties into the role of props objects in ReactJs.

For instance, consider a DisplayUser component. When no user object is passed to it, the app may crash. To prevent such errors, you can set default props as follows:

DisplayUser.defaultProps = { user:{ name:"", age:0 }};

So, when no user prop is passed, the component defaults to this value, utilizing the value of props objects. Default Props are essentially a safety net against missing or undefined props, playing a very important role in ReactJs.

Practical Examples of React Props

Example of passing and accessing props

Let’s look at an example. Here’s a simple Greeting component in a parent component, akin to passing attributes into an input element in HTML:

function App() {
      return (<Greeting name="John Doe"/>);
}

In this scenario, we’re sending a prop name, similar to an attribute, with a value of “Jane Doe” to the Greeting component, which can be compared to an input element.

Within Greeting, you can access the passed name prop akin to pulling values from a HTML input element:

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

In both instances, values are attached to properties or attributes and passed onward.

The output on the browser would be: Hello, John Doe!

In this example, Greeting is a component that reuses the passed name prop. This means you can greet any name by passing different values for name.

Using Props for displaying data in components

Props shine when it comes to displaying data in components. Specifically, they excel at generating dynamic data output. Consider an instance where you have a list of users and you wish to render their names – props become your go-to tool.

First, let’s define a user component:

function User(props) {
return <h2>{props.name}</h2>;
}

And in your App component, render a User instance for each user:

const users = [{name: 'Alex'}, {name: 'Bella'}, {name: 'Charlie'}];
return (<h2>{users.map(user => user.name)}</h2>);

This renders an h2 element for each user in the users array using props. This illustrates props’ capacity for producing dynamic and reusable components.

React Props – The Summary

Notable takeaways on React Props

A couple of fundamental takeaways on React Props include:

1. They streamline data flow from parent to child in a unidirectional manner using the props syntax, promoting structured, predictable data architecture.
2. Props encapsulate diverse data types, akin to HTML attributes, including JavaScript primitives, functions, and components which can be passed using the props objects.
3. Props are read-only within the component receiving them, which upholds data reliability and there is a possibility to use a more concise “spread” syntax.
4. Props’ dynamic behavior permits reactive UI updates according to changing prop data. They permit a handy form of destructuring where they don’t use any of their props directly.
5. The `children` prop facilitates composition in React, permitting nested child components. This method uses the value of props by defining the parameter as props objects.

In essence, a solid understanding of the props syntax and how to effectively use props objects is vital to effective React development.

Practicalities of using props in React development

Precisely utilizing props is a critical competence in React development. They provide a way to make components reusable with diverse data inputs, necessary for building interactive websites and essential react apps. Here’s why:

1. Component Customization: Applying different prop values can vastly vary a component’s behavior, appearance or content.
2. Clear Hierarchy: Props make data flow visible and easier to reason about since data only flows down from parent to child components.
3. Code Reusability: Props, like in popular websites built with React such as Facebook, Twitter, and Netflix, permit reusing components across different sections of your application, thereby keeping your code DRY(Don’t Repeat Yourself).
4. Composing Components: Combining components to create more complex UIs becomes a breeze with props as you will see in this tutorial on building and connecting components.

Building this robustness in React demands an efficient handling of props.

Frequently Asked Questions (FAQ)

What are the common errors while using props?

When using props in React, some common errors often crop up:

1. Mutating Props: Remember, in the context of ReactJS states and props, props should never be altered within a component. They are read-only and any attempts to modify them can lead to unpredictable results or even system failure.
2. Wrong Data Type: Despite JavaScript’s leniency with types, accidentally passing the wrong data types into a prop within your ReactJS application could lead to difficult-to-trace bugs.
3. Undefined Prop: It’s a common error to attempt to access a prop that hasn’t been established yet. If encountered, it will return ‘undefined’, potentially generating errors.
4. Not Passing Props to Super: When working with class components, always remember to pass props to super() within the constructor. Failure to do so results in this.props being undefined in the constructor, a common problem that might interfere with the operation of your ReactJS states.
5. Not Using Prop Types: Using prop types, which are considered a type of built-in object in ReactJS states’ ecosystem, can help catch bugs related to incorrect prop usage.

Such pitfalls are easily prevented with a strong understanding of how props work and the implementation of best practices. Ideally, knowledge gained from platforms such as Caltech Coding Bootcamp can be beneficial.

Can props be used in functional components?

Yes, props can be definitely used in functional components. In essence, props are passed to functional components as a single argument. This argument structure is part of what is known as props syntax. You can then unpack it, or destructure it, to access individual properties. Props thus enable functional components to become more versatile and reusable. Remember, just as in class components, props in functional components are also read-only. These are referred to as props objects which play a very important role.