The main difference between state and props is that props are immutable. This is why the container component should define the state that can be updated and changed, while the child components should only pass data from the state using props.

Using Props

When we need immutable data in our component, we can just add props to reactDOM.render() function in main.js and use it inside our component.
App.jsx

import React from 'react';

class App extends React.Component {
render() {
return (
<div>
<h1>{this.props.headerProp}</h1>
<h2>{this.props.contentProp}</h2>
</div>
);
}
}
export default App;

main.js

import React from 'react';
import ReactDOM from 'react-dom';
import App from './App.jsx';

ReactDOM.render(<App headerProp = "Header from props..." contentProp = "Content
from props..."/>, document.getElementById('app'));

export default App;

This will produce the following result.

Default Props

You can also set default property values directly on the component constructor instead of adding it to the reactDom.render() element.
App.jsx

import React from 'react';

class App extends React.Component {
render() {
return (
<div>
<h1>{this.props.headerProp}</h1>
<h2>{this.props.contentProp}</h2>
</div>
);
}
}
App.defaultProps = {
headerProp: "Header from props...",
contentProp:"Content from props..."
}
export default App;

main.js
import React from 'react';
import ReactDOM from 'react-dom';
import App from './App.jsx';

ReactDOM.render(<App/>, document.getElementById(‘app’));
Output is the same as before.

State and Props

The following example shows how to combine state and props in your app. We are setting the state in our parent component and passing it down the component tree using props. Inside the render function, we are setting headerProp and contentProp used in child components.
App.jsx

import React from 'react';

class App extends React.Component {
constructor(props) {
super(props);
this.state = {
header: "Header from props...",
content: "Content from props..."
}
}
render() {
return (
<div>
<Header headerProp = {this.state.header}/>
<Content contentProp = {this.state.content}/>
</div>
);
}
}
class Header extends React.Component {
render() {
return (
<div>
<h1>{this.props.headerProp}</h1>
</div>
);
}
}
class Content extends React.Component {
render() {
return (
<div>
<h2>{this.props.contentProp}</h2>
</div>
);
}
}
export default App;
main.js
import React from 'react';
import ReactDOM from 'react-dom';
import App from './App.jsx';

ReactDOM.render(<App/>, document.getElementById('app'));

The result will again be the same as in the previous two examples, the only thing that is different is the source of our data, which is now originally coming from the state. When we want to update it, we just need to update the state, and all child components will be updated. More on this in the Events chapter.

ReactJS – Props Validation

Properties validation is a useful way to force the correct usage of the components. This will help during development to avoid future bugs and problems, once the app becomes larger. It also makes the code more readable, since we can see how each component should be used.

Validating Props

In this example, we are creating App component with all the props that we need. App.propTypes is used for props validation. If some of the props aren’t using the correct type that we assigned, we will get a console warning. After we specify validation patterns, we will set App.defaultProps.
App.jsx

import React from 'react';

class App extends React.Component {
render() {
return (
<div>
<h3>Array: {this.props.propArray}</h3>
<h3>Bool: {this.props.propBool ? "True..." : "False..."}</h3>
<h3>Func: {this.props.propFunc(3)}</h3>
<h3>Number: {this.props.propNumber}</h3>
<h3>String: {this.props.propString}</h3>
<h3>Object: {this.props.propObject.objectName1}</h3>
<h3>Object: {this.props.propObject.objectName2}</h3>
<h3>Object: {this.props.propObject.objectName3}</h3>
</div>
);
}
}

App.propTypes = {
propArray: React.PropTypes.array.isRequired,
propBool: React.PropTypes.bool.isRequired,
propFunc: React.PropTypes.func,
propNumber: React.PropTypes.number,
propString: React.PropTypes.string,
propObject: React.PropTypes.object
}

App.defaultProps = {
propArray: [1,2,3,4,5],
propBool: true,
propFunc: function(e){return e},
propNumber: 1,
propString: "String value...",

propObject: {
objectName1:"objectValue1",
objectName2: "objectValue2",
objectName3: "objectValue3"
}
}
export default App;
main.js
import React from 'react';
import ReactDOM from 'react-dom';
import App from './App.jsx';

ReactDOM.render(<App/>, document.getElementById('app'));

So, this brings us to the end of blog. This Tecklearn ‘Props Overview in ReactJS’ blog helps you with commonly asked questions if you are looking out for a job in React JS and Front-End Development. If you wish to learn React JS and build a career in Front-End Development domain, then check out our interactive, React.js with Redux Training, that comes with 24*7 support to guide you throughout your learning period.

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Introduction to Web Development and React.js
• Fundamentals of React
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• Installation of React
• JSX and its use case
• DOM
• Virtual DOM and its working
• ECMAScript
• Difference between ES5 and ES6
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Components, JSX & Props
• React Elements
• Render Function
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• Class Component
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React State Management using Redux
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React & Redux
• The React Redux Node Package
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React Hooks
• Caveat of JavaScript classes.
• Functional components and React hooks
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• Basic hooks
• useState() hook
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• Fetch API data using useEffect() hook
• useContext() hook
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• What is GraphQL?
• Cons of Rest API
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• Express framework
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• Define Jest
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• What is React Native
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React with Redux Projects

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