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When we try to update the initial state of a component in React, it means that we want that initial state to change in response to user actions or system events.

When the initial state changes or updates, the information displayed on the browser also changes. This is because React renders the component again with the updated code.

setState()The function is the main React function that updates the nested state of the component.

After we set the initial state of the component, React setState()is the function that is called to initialize the new state. Because we need the user to trigger an event, we will setState()apply the next onClickfunction to listen for the action taken by the user and then render the updated state component.

We will now look at various examples that demonstrate how to update the initial state of nested components.

In this example, we will setState()update the initial state component using the method, we will update a single entry present in the array:

Code snippet ( App.js):

import React, { Component } from 'react'
class App extends Component {
constructor(props){
    super(props)

    // Set initial state
    this.state = {greeting :
        'Click the button to receive greetings'}

    // Binding this keyword
    this.updateState = this.updateState.bind(this)
}
updateState(){
    // Changing state
    this.setState({greeting :
        'Welcome!!!'})
}
render(){
    return (
    <div>
        <h2>Greetings Portal</h2>
        <p>{this.state.greeting}</p>
        {/* Set click handler */}
        <button onClick={this.updateState}>
        Click me!
        </button>
    </div>
    )
}
}
export default App;

Output:

After setting the initial state of the component, we need to first greetingbind the keyword to updateStatethe function so React will know which keyword to look for in the component and make the change.

We then use setStatethe function to encode greetingthe data we want the keyword to return.

Finally, we use an event listener with updateStatea function so that when the user clicks the button, the information on the browser is changed and updated.onClickClick me!

This example is more similar to the previous one. However here, we are dealing with multiple entries in the component state.

Code snippet ( App.js):

import React, { Component } from 'react'
class App extends Component {
constructor(props){
    super(props)

    // Set initial state
    this.state = {
    test: "Nil",
    questions: "0",
    students: "0"
    }

    // Binding this keyword
    this.updateState = this.updateState.bind(this)
}
updateState(){
    // Changing state
    this.setState({
        test: 'Programming Quiz',
        questions: '10',
        students: '30'
    })
}
render(){
    return (
    <div>
        <h2>Test Portal</h2>
        <p>{this.state.test}</p>

        <p>{this.state.questions}</p>

        <p>{this.state.students}</p>
        {/* Set click handler */}
        <button onClick={this.updateState}>
        Click me!
        </button>
    </div>
)
}
}
export default App;

Output:

After setting the first state, we bind this.statethe keyword. After that, we proceed to update the state of the elements in the array.

Because we are dealing with multiple elements, we put each item into a paragraph element so that it appears like a list when it is rendered on the web page.

In this example, we use props to update the initial state. Props is short for properties.

This method is ideal for tasks involving multiple items in arrays and complex data forms, and helps to update the state easily.

Just like in the example above, we App.jsencode in .

Code snippet ( App.js):

import React, { Component } from 'react'
class App extends Component {
static defaultProps = {
    testTopics : [
        'React JS', 'Node JS', 'Compound components',
        'Lifecycle Methods', 'Event Handlers',
        'Router', 'React Hooks', 'Redux',
        'Context'
    ]
}

constructor(props){
    super(props)

    // Set initial state
    this.state = {
    testName: "React js Test",
    topics: ''
    }

    // Binding this keyword
    this.updateState = this.updateState.bind(this)
}
listOfTopics(){
    return (
    <ul>
        {this.props.testTopics.map(topic => (
            <li>{topic}</li>
        ))}
    </ul>
    )
}

updateState(){
    // Changing state
    this.setState({
    testName: 'Test topics are:',
    topics: this.listOfTopics()
    })
}
render(){
    return (
    <div>
        <h2>Test Information</h2>
        <p>{this.state.testName}</p>
        <p>{this.state.topics}</p>
        {/* Set click handler */}
        <button onClick={this.updateState}>
        Click me!
        </button>
    </div>
    )
}
}
export default App;

Output:

We first testTopicspass multiple data in the array. Then we set the initial state of the data into testNamethe array.

After testNamebinding the keyword to updateState, we create a listOfTopicsfunction that returns testTopicsthe items in the array as topica list with state .

We then onClickuse the function alongside the event listener setState()so that when Click me!the button is punched, the list of items will be displayed in React js Testthe position of the initial state.

This is a numerical example where we want the initial value to increase. In this case, we want the initial state to increase rather than change.

Since we want the initial state to increment, we'll useState()pass it as a parameter in the function prevState, and useState()we'll use it in the arrow function.

Code snippet ( App.js):

import React, { Component } from 'react'

class App extends Component {

    constructor(props){
        super(props)

        // Set initial state
        this.state = {
            count: 0
        }

        // Binding this keyword
        this.updateState = this.updateState.bind(this)
    }

    updateState(){
        // Changing state
        this.setState((prevState) => {
            return { count: prevState.count + 1}
        })
    }

    render(){
        return (
            <div>
                <h2>Click Counter</h2>
                <p>You have clicked me {this.state.count} times.</p>
                {/* Set click handler */}
                <button onClick={this.updateState}>
                    Click me!
                </button>
            </div>
        )
    }
}

export default App;

Output:

We setStatecall the in function prevStateso that when the button is clicked, it identifies the last state the data was in and increments that state by 1, just as we returnset it in the array, increasing the count by 1.

There are multiple uses for updating a component's state in React. However, with the examples we have discussed, coders should be able to apply different use cases in any situation.