4 methods to force a re-render in React
Tags: react, abotwrotethis
Published: 2023-04-05 01:28:02

React is a popular front-end library used by developers across the world. It offers a lot of benefits over other JavaScript libraries and has an excellent documentation source. One of the best qualities of React is its performance optimizations. Using React, developers can create performant websites and web applications with reusable components, state management, and much more.

However, there may come a time when you need to force a re-render in React. In this article, we'll detail four techniques you can use to force a re-render in React. These techniques can help you get the most out of your React applications.

## Why Do You Need to Force a Re-Render in React?

Sometimes, you may need to update your app's state, which doesn't cause a re-render automatically. For instance, when updating a child component's state, like text inside a div tag, the parent component often won't receive updates. In such a case, we need to force a re-render to update the entire app's state.

Another situation that may require a forced re-render is when you make an API call that returns new data to the React component. In this scenario, it's guaranteed that the new data will be available in the component's state, but the component will not re-render automatically.

Now, let's dive into the techniques you can use to force a re-render in React.

## Technique #1 - Using setState in React

The easiest and most straightforward way of forcing a re-render in React is to use the setState method. The setState method is a built-in React method that we can use to update the app's state. Whenever we update the component's state using the setState method, React re-renders the component.

Here's how we can use setState to force a re-render of a React component:

```jsx
import React, {useState} from 'react';

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

  function handleClick() {
    setCount(count + 1);
    setCount(count + 1);
  }

  return (
    <div>
      <p>{count}</p>
      <button onClick={handleClick}>Increment Count</button>
    </div>
  );
}
```

In the above example, we initially set the count state to zero, and when the button is clicked, we're incrementing the count by 1 twice using two setCount methods. Since we're using the setCount method twice, React will force a re-render, and in this case, it will update the count value to 2.

## Technique #2 - Using ForceUpdate in React

The second way of forcing a re-render in React is to use the forceUpdate method. The forceUpdate method is another built-in React method that we can use to re-render a component manually.

Here's an example of how you can use the forceUpdate method to force a re-render in a React component:

```jsx
import React, {Component} from 'react';

class App extends Component {
  state = {count: 0};

  handleClick = () => {
    this.setState({count: this.state.count + 1});
  }

  handleForceUpdate = () => {
    this.forceUpdate();
  }

  render() {
    return (
      <div>
        <p>{this.state.count}</p>
        <button onClick={this.handleClick}>Increment Count</button>
        <button onClick={this.handleForceUpdate}>Force Update</button>
      </div>
    );
  }
}
```

In the above example, we have two buttons in the component. The first button increments the count state whenever clicked, whereas the second button manually calls the forceUpdate method to force a re-rendering of the component.

## Technique #3 - Using Hooks in React

Hooks are a new feature introduced in React 16.8, which allows us to use state and other React features without writing a class component. The useState method, which we discussed in the first technique, is an example of a hook.

Using hooks, we can also force a re-rendering of a component by updating a state variable that doesn't change its value. This technique works because React checks if the state variable has changed in case of state updates. Then, it assumes that it needs to re-render the component. 

Here's how you can use hooks to force a re-render in React:

```jsx
import React, {useState} from 'react';

function App() {
  const [count, setCount] = useState(0);
  const [dummyState, setDummyState] = useState(false);

  function handleClick() {
    setCount(count + 1);
    // the second setDummyState call doesn't change the value.
    setDummyState(!dummyState);
  }

  return (
    <div>
      <p>{count}</p>
      <button onClick={handleClick}>Increment Count</button>
    </div>
  );
}
```

In this example, we're using the useState hook again, but now we're also using a boolean variable called dummyState. The `dummyState` value is not changing its value anywhere in the component but firing alongside the state updates.

## Technique #4 - Using Unique Keys in a map Callback

When you're rendering a list of items with React, each item inside the list should have a `key` property that uniquely identifies it. The `key` property is used internally by React to keep track of which components need to be re-rendered when a component is updated.

You can sometimes use this `key` property to force a re-render in React. This technique can come in handy when you want to change the order of the list items in the state without changing their properties on the app.

Here's an example of how to use `key` to force a re-render:

```jsx
import React, {useState} from 'react';

function App() {
  const [list, setList] = useState([
    {id: 1, name: 'John'},
    {id: 2, name: 'Michael'},
  ]);

  function handleClick() {
    const updatedList = [...list];
    updatedList.reverse();

    // set the updated list into the state.
    setList(updatedList);
  }

  return (
    <div>
      <ul>
        {list.map(item => (
          // set the item.id to unique key property.
          <li key={item.id}>{item.name}</li>
        ))}
      </ul>
      <button onClick={handleClick}>Reverse List</button>
    </div>
  );
}
```

In this example, we have a list of objects stored in the state with unique IDs. Whenever the button is clicked, the list is reversed, and the list's state is updated. To force a re-render, we're using the `key` property with each item in the list, which signals to React that it should re-render the entire list.

## Conclusion

In conclusion, forcing a re-render in React is sometimes required for a better user experience or fixing a glitch in the app. It's good to know the techniques that we can use to force a re-render manually. In this article, we've discussed four techniques to re-render a React component: using setState, forceUpdate, hooks, and using a unique key property. These techniques will help you optimize your React app's performance and improve user experience.