6. Conditional Rendering

Conditional rendering is a technique in React that allows you to conditionally render different content or components based on certain conditions or states. It’s a powerful way to create dynamic user interfaces that respond to user interactions or changing data. There are multiple ways to achieve conditional rendering in React:

1. Using `if` Statements in React:

You can use regular JavaScript if statements to conditionally render content within the render method of your component.

import React, { Component } from 'react';

class ConditionalRender extends Component {
  render() {
    if (this.props.isLoggedIn) {
      return <p>Welcome, user!</p>;
    } else {
      return <p>Please log in to continue.</p>;
    }
  }
}

export default ConditionalRender;

2. Using Ternary Operator in React:

The ternary operator is a concise way to perform conditional rendering.

import React from 'react';

const ConditionalRender = (props) => {
  return (
    <div>
      {props.isLoggedIn ? <p>Welcome, user!</p> : <p>Please log in to continue.</p>}
    </div>
  );
};

export default ConditionalRender;

3. Using Logical AND Operator (`&&`) in React:

You can use the logical AND operator (&&) to conditionally render content.

import React from 'react';

const ConditionalRender = (props) => {
  return (
    <div>
      {props.isLoggedIn && <p>Welcome, user!</p>}
      {!props.isLoggedIn && <p>Please log in to continue.</p>}
    </div>
  );
};

export default ConditionalRender;

4. Using Element Variables in React:

You can conditionally assign JSX elements to variables and then use those variables within the render method.

import React, { Component } from 'react';

class ConditionalRender extends Component {
  render() {
    let message;
    if (this.props.isLoggedIn) {
      message = <p>Welcome, user!</p>;
    } else {
      message = <p>Please log in to continue.</p>;
    }

    return <div>{message}</div>;
  }
}

export default ConditionalRender;

5. Conditional Rendering of Components in React:

You can also conditionally render entire components based on conditions.

import React from 'react';
import WelcomeComponent from './WelcomeComponent';
import LoginComponent from './LoginComponent';

const ConditionalRender = (props) => {
  return (
    <div>
      {props.isLoggedIn ? <WelcomeComponent /> : <LoginComponent />}
    </div>
  );
};

export default ConditionalRender;

Conditional rendering is extremely versatile and allows you to create dynamic user interfaces that adjust based on various factors. You can use these techniques to display different content, components, or UI elements depending on the state of your application or user interactions.

The `map()` function for rendering lists

The map() function can be used not only for rendering lists of elements but also for conditionally rendering elements based on certain conditions. You can combine the map() function with conditional logic to dynamically generate and render components or elements based on the data and conditions. Here’s how you can use the map() function for conditional rendering of lists in React:

import React from 'react';

const ItemList = (props) => {
  const items = props.items;

  return (
    <ul>
      {items.map((item, index) => (
        <li key={index}>
          {item.completed ? <s>{item.name}</s> : item.name}
        </li>
      ))}
    </ul>
  );
};

export default ItemList;

In this example, the ItemList component receives an array of items as a prop. Each item has a name and a completed property. The map() function is used to iterate over the items array and conditionally render an <s> (strikethrough) element around the item’s name if the completed property is true.

Usage of the ItemList component might look like this:

import React from 'react';
import ItemList from './ItemList';

const ParentComponent = () => {
  const items = [
    { name: 'Task 1', completed: true },
    { name: 'Task 2', completed: false },
    { name: 'Task 3', completed: true },
  ];

  return (
    <div>
      <h2>List of Items:</h2>
      <ItemList items={items} />
    </div>
  );
};

export default ParentComponent;

By using the map() function with conditional rendering, you can create dynamic lists where the appearance of each item is determined by the values in your data. This allows you to build user interfaces that adjust and display information based on specific conditions.

Using `key` prop for efficient list rendering

The key prop is a special attribute that you provide when rendering lists of elements in React. It helps React identify individual elements efficiently and manage their state and updates effectively during rendering. The key prop is essential for performance and correct behavior when rendering dynamic lists.

Here’s why the key prop is important and how to use it:

1. Uniqueness: Each key should be unique among sibling elements in a list. React uses the key to keep track of which elements have changed, been added, or been removed.

2. Reconciliation: When a list is updated, React uses the key to determine if an element has changed position, if new elements have been added, or if existing elements have been removed. This process is known as reconciliation.

3. Performance: Using proper key values helps React optimize updates and avoids unnecessary re-renders, leading to better performance.

4. No Business Logic: The key prop is for React’s internal use and should not be used to convey business logic or data. It’s not passed to the component as a prop.

Here’s an example of using the key prop for efficient list rendering:

import React from 'react';

const ItemList = (props) => {
  const items = props.items;

  return (
    <ul>
      {items.map((item, index) => (
        <li key={item.id}>{item.name}</li>
      ))}
    </ul>
  );
};

export default ItemList;

In this example, the key prop is set to item.id, assuming that each item has a unique id property. Using a unique identifier as the key ensures that React can accurately track changes in the list and optimize rendering.

Usage of the ItemList component might look like this:

import React from 'react';
import ItemList from './ItemList';

const ParentComponent = () => {
  const items = [
    { id: 1, name: 'Item 1' },
    { id: 2, name: 'Item 2' },
    { id: 3, name: 'Item 3' },
  ];

  return (
    <div>
      <h2>List of Items:</h2>
      <ItemList items={items} />
    </div>
  );
};

export default ParentComponent;

By providing a unique key value for each item in your list, you ensure that React can efficiently manage updates and maintain a high level of performance when rendering dynamic lists.

Last updated on Sep 18, 2023

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6. Conditional Rendering

1. Using if Statements in React: