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ReactJS | Stateless Component

ReactJS | Stateless Component


Hello folks! welcome back to a new section of our tutorial on ReactJS. In this section of our tutorial on ReactJS, we will be studying about ReactJS Stateless Component.

React component that has an internal state management is called Stateful Component and React component without any internal state is called Stateless Component. React recommends that you create and also use as many Stateless Component as possible and create stateful components only when it is absolutely necessary. Also, React does not share the state with child components. The information needs to be passed to the child component through child's properties.

Following below is an example to pass date to the FormattedDate component -

<FormattedDate value={this.state.item.spend_date} />

The general idea isn't to overcomplicate the application logic and use advanced features only when necessary.

Create a Stateful Component

Let us create a React application to display the current date and time.

First, create a new React application, react-clock-app using Create React App or Roll-up bundler by following the instructions given in Creating a React application tutorial.

Next, open the application in your favorite editor.

Next, create an src folder beneath the root directory of the application.

Next, create components folder beneath src folder.

Create a file, Clock.js under src/component folder and start editing.

Next, import React library.

import React from 'react';


Next, create Clock component.

class Clock extends React.Component { 
   constructor(props) { 
      super(props); 
   } 
}

Next, initialize state with current date and time.

constructor(props) { 
   super(props); 
   this.state = { 
      date: new Date() 
   } 
}

Next, add a method, setTime() to update the current time.

setTime() { 
   console.log(this.state.date); 
   this.setState((state, props) => (
      {
         date: new Date() 
      } 
   )) 
}

Next, use the JavaScript method, setInterval and call the setTime() method every second to make sure that the component's state is updated every second.

constructor(props) { 
   super(props); 
   this.state = { 
      date: new Date() 
   } 
   setInterval( () => this.setTime(), 1000); 
}

Next, create a render function.

render() {
}
Next, update the render() method to show the current time.
render() {
   return (
      <div><p>The current time is {this.state.date.toString()}</p></div>
   );
}

Finally, export the component.

export default Clock;

The complete code of the Clock component is as follows -

import React from 'react';

class Clock extends React.Component {
   constructor(props) {
      super(props);
      this.state = {
         date: new Date()
      }      
      setInterval( () => this.setTime(), 1000);
   }
   setTime() {
      console.log(this.state.date);
      this.setState((state, props) => (
         {
            date: new Date()
         }
      ))
   }
   render() {
      return (
         <div>
            <p>The current time is {this.state.date.toString()}</p>
         </div>
      );
   }
}
export default Clock;

Next, create a file, index.js beneath the src folder and use Clock component.

import React from 'react';
import ReactDOM from 'react-dom';
import Clock from './components/Clock';

ReactDOM.render(
   <React.StrictMode>
      <Clock />
   </React.StrictMode>,
   document.getElementById('root')
);

Finally, create a public folder under the root folder and create index.html file.

<!DOCTYPE html>
<html lang="en">
   <head>
      <meta charset="utf-8">
      <title>Clock</title>
   </head>
   <body>
      <div id="root"></div>
      <script type="text/JavaScript" src="./index.js"></script>
   </body>
</html>

Next, serve the application making use of npm command.

npm start

Next, open the web browser and then enter http://localhost:3000 in the address bar and press enter. The application will display the time and update it every second.

The current time is Mon Jan 17 2022 10:10:18 GMT+0530(West African Time)

The above application works correctly but throws an error in the console.

Can't call setState on a component that is not yet mounted.

The error message shows that the setState has to be called only after the component is mounted.


What is Mounting

React component has what is called a life-cycle and mounting is one of the stages in the life-cycle. We will learn more about life-cycle in our upcoming tutorials.

Introduce State in Expense Manager App

Let us introduce state management in the expense manager application by adding a simple feature to remove an expense item.

Open expense-manager application in your favorite editor.

Next, open ExpenseEntryItemList.js file.

Next, initialize the component state with the expense items passed into the components via properties.

this.state = { 
   items: this.props.items 
}

Next, add the Remove label in the render() method.

<thead>
   <tr>
      <th>Item</th>
      <th>Amount</th>
      <th>Date</th>
      <th>Category</th>
      <th>Remove</th>
   </tr>
</thead>

Next, update the lists in the render() method to include the remove link. Also use items in the state (this.state.items) instead of items from the properties (this.props.items).

const lists = this.state.items.map((item) =>
   <tr key={item.id} onMouseEnter={this.handleMouseEnter} onMouseLeave={this.handleMouseLeave}>
      <td>{item.name}</td>
      <td>{item.amount}</td>
      <td>{new Date(item.spendDate).toDateString()}</td>
      <td>{item.category}</td>
      <td><a href="#" onClick={(e) =>  this.handleDelete(item.id, e)}>Remove</a></td>
   </tr>
);

Next, apply the handleDelete method, which will remove the relevant expense item from the state.

handleDelete = (id, e) => {
   e.preventDefault();
   console.log(id);

   this.setState((state, props) => {
      let items = [];

      state.items.forEach((item, idx) => {
         if(item.id != id)
            items.push(item)
      })
      let newState = {
         items: items
      }
      return newState;
   })
}

Here,

  • Expense items are gotten from the current state of the component.
  • Current expense items are looped over to find the item referred by the user using id of the item.
  • Create a new item list with all of the expense item except the one referred by the user.

Next, include a new row to display the total expense amount.

<tr>
   <td colSpan="1" style={{ textAlign: "right" }}>Total Amount</td>
   <td colSpan="4" style={{ textAlign: "left" }}>
      {this.getTotal()}
   </td> 
</tr>

Next, implement the getTotal() method to calculate the total expense amount.

getTotal() {
   let total = 0;
   for(var i = 0; i < this.state.items.length; i++) {
      total += this.state.items[i].amount
   }
   return total;
}

The complete code of the render() method is as follows -

render() {
   const lists = this.state.items.map((item) =>
      <tr key={item.id} onMouseEnter={this.handleMouseEnter} onMouseLeave={this.handleMouseLeave}>
         <td>{item.name}</td>
         <td>{item.amount}</td>
         <td>{new Date(item.spendDate).toDateString()}</td>
         <td>{item.category}</td>
         <td><a href="#" 
            onClick={(e) =>  this.handleDelete(item.id, e)}>Remove</a></td>
      </tr>
   );
   return (
      <table onMouseOver={this.handleMouseOver}>
         <thead>
            <tr>
               <th>Item</th>
               <th>Amount</th>
               <th>Date</th>
               <th>Category</th>
               <th>Remove</th>
            </tr>
         </thead>
         <tbody>
            {lists}
            <tr>
               <td colSpan="1" style={{ textAlign: "right" }}>Total Amount</td>
               <td colSpan="4" style={{ textAlign: "left" }}>
                  {this.getTotal()}
               </td> 
            </tr>
         </tbody>
      </table>
   );
}


The updated code of ExpenseEntryItemList is as follows -

import React from 'react';
import './ExpenseEntryItemList.css';

class ExpenseEntryItemList extends React.Component {
   constructor(props) {
      super(props);
      this.state = {
         items: this.props.items
      }
      this.handleMouseEnter = this.handleMouseEnter.bind();
      this.handleMouseLeave = this.handleMouseLeave.bind();
      this.handleMouseOver = this.handleMouseOver.bind();
   }
   handleMouseEnter(e) {
      e.target.parentNode.classList.add("highlight");
   }
   handleMouseLeave(e) {
      e.target.parentNode.classList.remove("highlight");
   }
   handleMouseOver(e) {
      console.log("The mouse is at (" + e.clientX + ", " + e.clientY + ")");
   }
   handleDelete = (id, e) => {
      e.preventDefault();
      console.log(id);
      this.setState((state, props) => {
         let items = [];
         state.items.forEach((item, idx) => {
            if(item.id != id)
               items.push(item)
         })
         let newState = {
            items: items
         }
         return newState;
      })
   }
   getTotal() {
      let total = 0;
      for(var i = 0; i < this.state.items.length; i++) {
         total += this.state.items[i].amount
      }
      return total;
   }
   render() {
      const lists = this.state.items.map((item) =>
         <tr key={item.id} onMouseEnter={this.handleMouseEnter} onMouseLeave={this.handleMouseLeave}>
            <td>{item.name}</td>
            <td>{item.amount}</td>
            <td>{new Date(item.spendDate).toDateString()}</td>
            <td>{item.category}</td>
            <td><a href="#" 
               onClick={(e) =>  this.handleDelete(item.id, e)}>Remove</a></td>
         </tr>
      );
      return (
         <table onMouseOver={this.handleMouseOver}>
            <thead>
               <tr>
                  <th>Item</th>
                  <th>Amount</th>
                  <th>Date</th>
                  <th>Category</th>
                  <th>Remove</th>
               </tr>
            </thead>
            <tbody>
               {lists}
               <tr>
                  <td colSpan="1" style={{ textAlign: "right" }}>Total Amount</td>
                  <td colSpan="4" style={{ textAlign: "left" }}>
                     {this.getTotal()}
                  </td> 
               </tr>
            </tbody>
         </table>
      );
   }
}
export default ExpenseEntryItemList;

Next, update the index.js and then add the ExpenseEntryItemList component.

import React from 'react';
import ReactDOM from 'react-dom';
import ExpenseEntryItemList from './components/ExpenseEntryItemList'

const items = [
   { id: 1, name: "Pizza", amount: 80, spendDate: "2020-10-10", category: "Food" },
   { id: 2, name: "Grape Juice", amount: 30, spendDate: "2020-10-12", category: "Food" },
   { id: 3, name: "Cinema", amount: 210, spendDate: "2020-10-16", category: "Entertainment" },
   { id: 4, name: "Java Programming book", amount: 242, spendDate: "2020-10-15", category: "Academic" },
   { id: 5, name: "Mango Juice", amount: 35, spendDate: "2020-10-16", category: "Food" },
   { id: 6, name: "Dress", amount: 2000, spendDate: "2020-10-25", category: "Cloth" },
   { id: 7, name: "Tour", amount: 2555, spendDate: "2020-10-29", category: "Entertainment" },
   { id: 8, name: "Meals", amount: 300, spendDate: "2020-10-30", category: "Food" },
   { id: 9, name: "Mobile", amount: 3500, spendDate: "2020-11-02", category: "Gadgets" },
   { id: 10, name: "Exam Fees", amount: 1245, spendDate: "2020-11-04", category: "Academic" }
]
ReactDOM.render(
   <React.StrictMode>
      <ExpenseEntryItemList items={items} />
   </React.StrictMode>,
   document.getElementById('root')
);

Next, serve the application by making use of npm command.

npm start

Next, open the web browser and then enter http://localhost:3000 in the address bar and press enter.

Finally, to remove an expense item, click on the corresponding remove link. It's going to remove the corresponding item and refresh the user interface as shown below -



Alright guys! This is where we are going to be rounding up for this tutorial. In our next tutorial, we will be discussing about State Management using React Hooks.

Feel free to ask your questions where necessary and we will attend to them as soon as possible. If this tutorial was helpful to you, you can use the share button to share this tutorial.

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Thanks for reading and bye for now.

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