React Force Rendering: Complete Tutorial

As a developer, when building user interfaces with a library like React, released in 2013 , your application may slow down as it becomes more complex. React re-renders components whenever their state or props change, even if the changes are insignificant or irrelevant. This can cause your app to waste valuable resources and cause unnecessary delays for your users. To resolve this issue, it is essential to explore techniques that can help you implement rerendering in a way that significantly reduces the number of rerenders and improves the performance of your React application.

In this article, I'll delve into React's forced re-rendering, which is a way to trigger the re-rendering of a component manually. I will also discuss how to implement this technique in your React application using various methods such as changing state, changing a component's key, and using the forceUpdate method. By understanding why and when you might need this technique, you can use it to build faster, more efficient React applications that provide a better user experience for your users.

Let's dive!

What is React Force rerendering?

React forced rerendering is a technique used to force a component to rerender even when there are no changes to its props or state. This can be useful when you want to update the component based on external factors that are not directly related to the internal state of the component. For example, if you have a component that displays the current time, you might want to force it to re-render every second to update the displayed time.

When does React re-render?

Let's dig a little deeper and see when React re-renders a component.

How to implement forced re-rendering in React?

There are several ways to force a component to re-render in React. Let's now look at some ways we can implement forced re-renders in React.

Prerequisites

To implement the forced react renderer successfully, you must have the following:

• Node.js : The latest version of Node.js on your machine.
• A code editor : Any IDE that supports React.
• React Library: The latest version of React on your machine.

Update status

In React, you can force a component to re-render by updating its state. Here is an example code snippet:

 import React, { useState } from 'react';

 function Counter {
 const (count, setCount) = useState(0);

 function increment {
 setCount(count + 1);
 }

 function forceRender {
 setCount(count);
 }

 return (
 <div>
 <p>Count: {count}</p> 
<button onClick={increment}>Increment</button>
 <button onClick={forceRerender}>Force Rerender</button>
 </div>
 );
 }

In this example, I have a Counter component that renders a count value and two buttons. The increment function updates the count state by adding 1. The forceRerender function also updates the count state, but sets the value to the current count, effectively doing nothing. However, because the state has changed, React will re-render the component and the count value will be updated.

Use the forceUpdate method

Another way to force a new render in React is using the forceUpdate method, available in the class components. Here is an example code snippet:

 import React, { Component } from 'react';

 class MyComponent extends Component {
 constructor(props) {
 super(props);
 this.state = { count: 0 };
 }

 increment {
 this.setState({ count: this.state.count + 1 });
 }

 forceRender {
 this.forceUpdate;
 }

 render {
 return (
 <div> 
<p>Count: {this.state.count}</p>
 <button onClick={ => this.increment }>Increment</button>
 <button onClick={ => this.forceRerender }>Force Rerender</button>
 </div>
 );
 }
 }

In this example, I have a component of the MyComponent class that also renders a count value and two buttons. The increment function updates the counting state by adding 1. The forceRerender function calls the forceUpdate method to force a re-render of the component. This method should be used less, as it may be less efficient than updating the state and lead to unnecessary re-renders.

Change the main property of a component

Additionally, changing a component's key property can also trigger a re-render in React. The key property is a special attribute that React uses to identify list elements and help optimize updates.

Here is an example code snippet that demonstrates how changing the key property of a child component can trigger a re-render:

 import React, { useState } from 'react';

 function List {
 const (items, setItems) = useState(('apple', 'banana', 'cherry'));

 function shuffleItems {
  const shuffled = (...items).sort( => Math.random - 0.5);
  setItems(shuffled);
 }

 return (
  <div>
   <button onClick={shuffleItems}>Shuffle Items</button>
   <ul>
    {items.map((item, index) => (
     <li key={item}>{item}</li>
    ))}
   </ul>
  </div>
 );
 }

In this example, I have a List component that renders a list of items and a button to shuffle the items randomly. The key property for each item is set to the item's own value, which means that if the order of the items changes, React will re-render the list.

When the shuffleItems function is called, it creates a new array of items by shuffling the existing array. When the new array is set as the state, the List component is re-rendered and React detects that each item's key property has changed. React then updates the list to reflect the new order of items.

Changing the key property can be useful to trigger a re-render when the data in a component changes but the state does not. However, it should be used with caution as changing the core support too frequently can lead to unnecessary re-renders and degrade performance.

When to use React Force re-rendering?

While forced re-renders can be useful in certain situations, they should not be used frequently as they can be less efficient than letting React handle updates automatically. It is generally recommended to use forced re-rendering only when necessary and consider alternative approaches such as using state or props to trigger updates.

Some common use cases for React Force re-rendering include:

• Update a component based on external data or events that are not directly related to the component's state or properties.
• Trigger a re-render of an updated component via a third-party library or non-React code.
• Updating a component that has been disassembled and reassembled.

Optimizing your new rendering

Here are some tips for optimizing re-renders in React:

Use the shouldComponentUpdate lifecycle method

This method allows you to control when a component should be updated by returning a boolean value. By default, shouldComponentUpdate returns true, which means a component will always update when its state or props change. However, you can override this method to implement custom logic that determines when a component should be updated. For example, if a component only needs to be updated if a specific property changes, you can compare the previous property value to the new property value in shouldComponentUpdate and return false if they are equal.

 class MyComponent extends React.Component {
 shouldComponentUpdate(nextProps, nextState) {
  // compare the props and state of the current and next component
  // only return true if they are different
  return this.props.someProp !== nextProps.someProp
     this.state.someState !== nextState.someState;
 }

 render { 
return <div>{this.props.someProp}</div>;
 }
 }

Use PureComponent or React.memo

PureComponent is a built-in React component that implements shouldComponentUpdate with a shallow comparison of props and state. This means that if a PureComponent's props and state have not changed, it will not be re-rendered. React.memo is a higher-order component that can be used to optimize functional components in the same way as PureComponent.

 class MyPureComponent extends React.PureComponent {
 render {
  return <div>{this.props.someProp}</div>;
 }
 }

 const MyMemoComponent = React.memo(function MyMemoComponent(props) {
 return <div>{props.someProp}</div>;
 });

Avoid unnecessary state updates

Updating the state triggers a re-render of the component. Therefore, you should avoid updating the state unnecessarily. For example, if a component displays a list of items and you only need to update the list when adding a new item, avoid calling setState when deleting or updating an item.

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

  this.state = {
   items:
  };
 }

 handleAddItem = (item) => {
  this.setState(prevState => {
   return {items: (...prevState.items, item)};
  });
 }

 render {
  return (
   <div>
    {this.state.items.map(item => <div key={item.id}>{item.name}</div>)}
    <button onClick={ => this.handleAddItem({id: 1, name: 'New Item'})}>Add Item</button>
   </div>
  );
 }
 }

Use Key Prop for Lists

When rendering lists of components, React uses the key property to track the identity of each component. If a component's key changes, React will treat it as a new component and re-render it. Therefore, you must use a stable and unique key for each component in the list to avoid unnecessary re-renders.

 class MyComponent extends React.Component {
 render {
  const items = ({id: 1, name: 'Item 1'}, {id: 2, name: 'Item 2'}, {id: 3, name: 'Item 3'});

  return (
   <div>
    {items.map(item => <div key={item.id}>{item.name}</div>)}
   </div>
  );
 }
 }

Use the shouldUpdate callback in useMemo and useCallback hooks

The useMemo and useCallback hooks can be used to memorize the result of a function or calculation. However, by default they will recalculate the result on each render. You can pass a second argument to useMemo or useCallback, an array of dependencies. The hook will only recompute the result if a dependency changes. If you have expensive calculations, you can use the shouldUpdate callback to implement custom logic that determines when the calculation should be updated.

 function MyComponent(props) {
 const (count, setCount) = React.useState(0);

 const expensiveValue = React.useMemo( => {
  // do some expensive computation here
  return count * 10;
 }, (count), (prev, next) => {
  // only update the computation if the count has increased by more than 5
  return (next - prev) > 5;
 });

 const handleClick = React.useCallback( => {
  setCount(prevCount => prevCount + 1);
 }, );

 return ( 
<div>
 <div>Count: {count}</div>
 <div>Expensive Value: {expensiveValue}</div>
 <button onClick={handleClick}>Increment Count</button>
 </div>
 );
 }

By implementing these optimizations, you can reduce the number of unnecessary re-renders in your React application and improve performance. These are just examples; The specific implementation will depend on your application needs.

Conclusion

In conclusion, re-rendering is an essential concept in React development as it determines when a component should be updated in response to changes in its state or props. React's virtual DOM engine and reconciliation process are designed to be efficient and optimized for performance, making it easy to build fast, responsive applications.

However, sometimes it may be necessary to force a re-render to update the UI when certain events occur. In this article, we explore some methods you can use to force a re-render in React, including changing state, changing a component's key, and using the forceUpdate method.

It is important to use these methods wisely to avoid excessive re-rendering, as this can impact the performance of your application. By following best practices and understanding when and why React re-renders components, you can build more efficient and faster React applications.

If you liked this article about React, check out these topics;

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• Why is React so popular?
• What you need to know about react
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