Using React Force Rerender in Your Application: When and Why?

As we all know, React is one of the most popular Javascript libraries for creating front-end applications. The key aspect contributing to React's success is its smooth browsing experience when creating websites. 

Also, the feature of this framework is that it only modifies the parts of the user interface that require to be updated. 

The React library has a collection of predefined methods for completing renderings, processing changes, and so on. React rerenders when the keys of a state, prop, or element change. However, in other cases, we must forcefully rerender the component. 

There are many ways you can force a React component to rerender, including methods offered by React specifically for this task.

In this article, you will learn about React force rerender and how and when you should force a React component to rerender.

Let's start!

What is React rerendering?

If we know about rendering in React, we can better understand rerendering. Rendering occurs when a component appears for the first time on the user's screen. 

Rerendering in react is defined as any additional render after a component's initial render, i.e., the second or subsequent render of a component already visible on the screen.

Rerendering occurs when React has to update the app with new data. This typically happens due to a user interacting with the app, external data arriving via an asynchronous request or a subscription mechanism.

Non-interactive apps won't rerender because they don't have any asynchronous data changes; thus, they don't need to worry about rerender speed optimization.

What is React force rerender?

React force rerendering makes a component render again even if its props or state remain unchanged. When you wish to update a component based on outside variables unrelated to the component's internal state, this can be helpful. 

For example, you could force a component that displays the current time to rerender every second to refresh the time shown.

In React, there are various ways to make a component rerender. Let's see a few strategies for implementing React force rerender.

When does React rerender itself?

Even though React force rerendering can be advantageous in some circumstances, doing so can be less effective than letting React handle updates naturally. It is generally advised only to use React force rerender when necessary and to consider other options, such as leveraging state or props to trigger changes.

The typical use cases of React force rerender include:

State changes

A component will rerender itself if its state changes. It typically occurs in a callback or useEffect hook. The root source of all rerenders is state changes.

Parent rerenders

If a component's parent rerender, the component will also rerender. Or, if we take a different approach, every child of a component is rendered again when it is rerendered. The rerender of a child does not cause the rerender of a parent; it always proceeds "down" the tree.

React hooks changes

The component using the hook "belongs" to anything that happens inside of it. Here, the same guidelines for Context and State changes apply:

• A state change within the hook will cause the "host" component to render itself again in an unavoidable manner.
• If the hook uses Context and Context value changes, it will inevitably cause the "host" component to be rendered again.

Hooks may be chained. The same criteria apply to each and every hook in the chain because each one still "belongs" to the "host" component.

Context changes

Even if they don't directly use the modified section of the data, all components that use this Context will rerender when the value in Context Provider changes. Memoization cannot directly prevent the rerenders, but some workarounds can simulate them.

Why are React components not rerendering?

Forcing a React component to rerender is not recommended in general, even when React fails to refresh the components naturally. Before attempting to force a rerender, we should examine our code.

Incorrectly updated state in React

React only rerenders when we invoke the setState() function related to that state to update its value; doing so manually is discouraged and will result in no changes being visible to React. The component will not be rerendered as a result.

Incorrectly updated props

Props are attributes associated with that state; wrongly altering them without the necessary state changes will not have the desired effect on component rerendering.

The reference to the props remained the same

React performs a shallow comparison to determine whether the current state and following state objects and the current and next props are comparable. If the keys in those props or states had the same value after the update, React would not have rendered them again.

How to do React force rerendering?

A React component rerenders itself if its state, props, or component keys change. Any of the procedures above must follow to render a component forcefully. Aside from this, React offers particular methods for this purpose in class-based React components. 

This does not imply that we can't do any of the steps above to force a rerender in class-based React components. However, we must manually carry out any steps above when dealing with React functional components.

Let's now look at alternative strategies for force rerendering a React component.

React force rerender by changing the component state

As previously discussed, we can force a React component to render by altering its state. The useState hook is used with functional components to create a state. The state and a function to update the state are returned in an array. 

In this situation, we can maintain the state values while encapsulating them in a new object such that React interprets them as having changed and causing a rerender. To better understand the code, let's analyze it:

Copy
1      import React, { useState, useEffect } from "react";
2    
3    function StateUpdate() {
4      const [state, setState] = React.useState({value: 10});
5    
6      function forceUpdate () {
7          setState(prev => {
8              return {...prev}
9          })
10      }
11    
12      useEffect(() => {
13        console.log('Rerender');
14      })
15    
16      return (
17        <button onClick={forceUpdate}>Button (State update)</button>
18      );
19    }
20     

We built the function rerenderForcefully in the code above to update the state. We updated the component's state within the function using the setState function. The function is connected to a button. 

We use the useEffect hook to listen for rerenders. Every time we click the button, the component is rendered, and the console is updated with "Rerender."

We put the data within a new object rather than altering them. React interprets this as a change in the state because the heap memory reference has been updated to reflect the new object.

React force rerender using the forceUpdate method

When using a class-based React component, we can forcefully rerender the component by using the official React method. We can use the forceUpdate component to execute the class's render function. It can be applied inside a straightforward class function or an event listener. 

You can use it as follows:

Copy
1     import React from 'react'
2    
3    class ForceUpdateMethod extends React.Component {
4      handleClick() {
5        this.forceUpdate();
6      }
7    
8      componentDidUpdate() {
9        console.log('Rerender');
10      }
11    
12      render() {
13        return <button onClick={this.handleClick.bind(this)}>Button (forceUpdate method)</button>;
14      }
15    }
16     

We've written a method handleClick in the code above that invokes the forceUpdate method. A button has the method handleClick connected to it. Utilizing the componentDidUpdate function, we watch for redraws. The component redraws each time we click the button, and the log "Rerender" is recorded in the console.

This approach does have a limitation. It can not force the child components to be rendered. This is because the shouldComponentUpdate function is also used for child components, which prevents rerendering. As a result, it can only be used to render the current component forcefully.

React force rerender using a custom React hook

The entire procedure we performed before can be contained inside a unique React hook. We can use the custom hook instead of writing logic for each component, making our code more comprehensible and understandable. Future React updates will also increase the effectiveness of hooks. For example, before compilation, components might be folded.

Let's add a special hook to force a React component to rerender itself:

Copy
1     function useForceRerender() {
2      const [state, setState] = React.useState({ value: 10 });
3    
4      function rerenderForcefully() {
5        setState((prev) => {
6          return { ...prev };
7        });
8      }
9    
10      return rerenderForcefully;
11    }
12     

Our hook accepts no arguments and returns a function, which our component will call to render. The logic we wrote within the custom hook is the same reasoning we used previously.

We can utilize our custom React hook inside any component by importing it as follows:

Copy
1     function StateUpdate() {
2      const forceUpdate = useForceUpdate();
3    
4      useEffect(() => {
5        console.log('Rerender');
6      })
7    
8      return <button onClick={forceUpdate}>Button (Custom hook)</button>;
9    }
10     

The useForceUpdate hook returns a function. The function is linked with a button. Using the useEffect hook, we listen for renderings. When we click the button, the component is rendered, and 'Rerender' is logged into the console.

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In this article we learned about React force rerendering and the ways to implement it.  

Using these techniques sparingly is crucial to prevent over-rendering, which can harm your application's performance. You can create more effective and quick React apps by adhering to best practices and comprehending when and why React re-renders components.

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