How to Trigger Re-renders in React

React uses a virtual DOM to minimize the number of costly DOM operations required to update your UI. It compares component state and props to determine if an actual re-render is needed. However, there may be times when you need to manually trigger a re-render in React. In this guide, we'll explore the main ways to force a component to re-render in React.

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Using the useState Hook

The easiest way to trigger a re-render is by updating state via the useState hook. For example:


import { useState } from 'react';

function MyComponent() {
  const [count, setCount] = useState(0);

  const forceUpdate = () => {
    setCount(prevCount => prevCount + 1);
  }
  
  return (
    <button onClick={forceUpdate}>Force Re-render</button> 
  )
}

Calling setCount will update the state and queue a re-render. This is useful for refreshing data.

Calling forceUpdate()

Class components expose the forceUpdate() method to force a re-render. For example:


class MyComponent extends React.Component {
  constructor(props) {
    super(props);
    this.forceUpdateHandler = this.forceUpdateHandler.bind(this);
  }
  
  forceUpdateHandler() {
    this.forceUpdate();
  }

  render() {
    return <button onClick={this.forceUpdateHandler}>Force Re-render</button>
  }
}

This will re-render the component even if state/props haven't changed.

Updating Context from Parent

If a component consumes context, forcing an update to the context value from a parent will trigger a re-render. For example:


// Context.js

export const MyContext = React.createContext();

// Parent.js 

import { MyContext } from './Context';

function Parent() {
  const [count, setCount] = useState(0);

  return (
    <MyContext.Provider value={{count}}>
      <Child />
      <button onClick={() => setCount(c => c + 1)}>
        Update Context
      </button>
    </MyContext.Provider>
  )
}

// Child.js

import { MyContext } from './Context';

function Child() {
  return (<div>{useContext(MyContext)}</div>);
}

Updating count in Parent will propagate to Child and force Child to re-render.

Using an Effect Hook

You can use the useEffect hook to trigger a re-render imperatively. For example:

  
function MyComponent() {
  const [count, setCount] = useState(0);

  useEffect(() => {
    const id = setInterval(() => {
      setCount(c => c + 1); 
    }, 1000);
    
    return () => clearInterval(id);
  }, []);

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

This will re-render every second as the interval updates state.

Calling Render Directly

You can manually call render() on a class component instance. For example:


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

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

  render() {
    return <div>{this.state.count}</div>; 
  }
}

This lets you separate the state update and re-render calls.

Memoizing Components

Wrapping a component in React.memo or useMemo will control re-rendering based on prop changes. For example:


// Only re-render if props change 
const MyComponent = React.memo(function MyComponent(props) {
  /*...*/
});

// Only re-render if deps change  
const MyComponent = useMemo(() => {
  return <div>Hello</div>
}, []);

This can prevent unnecessary re-renders.

When to Re-render

Some cases where you may need to force a re-render include:

Refreshing data from an API
Resetting component state
Animating based on imperative commands
Debugging update issues

Avoid re-rendering too frequently as it impacts performance. Only re-render when necessary.

Caveats

Some drawbacks of forcing re-renders:

Can harm optimization from virtual DOM checking
Can cause unnecessary UI thrashing
Bypasses lifecycle methods like shouldComponentUpdate
Triggers effects unconditionally

Use judiciously and measure the performance impact.

Summary

In summary, the main ways to trigger re-renders are:

Updating state with useState
Calling forceUpdate() in class components
Changing context from a parent component
Side effects with useEffect
Direct render() calls in classes

Re-rendering should be avoided when possible, but is sometimes useful. Just take care to measure performance impact.

Other Resources

For more on re-rendering in React, see:

Hopefully this guide gives you some ideas on how to think about re-renders in React apps and how to trigger them when needed.

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About the author: Daniel West

Tech Blogger & Researcher for JBI Training