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Learn how to effectively update DOM elements in React while running a time-intensive function using `setTimeout()` and `useEffect`.
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How to Update DOM Elements in React with setTimeout() for Real-time Feedback

When coding in React, there may be occasions when you need to manage long-running calculations and simultaneously show updates on the user interface. A common challenge developers face is that DOM elements often don't update until after the entire computation finishes. This can lead to frustration, especially when users want real-time feedback on ongoing processes.

In this guide, we will explore how to use setTimeout() and useEffect() to update the DOM elements while executing time-consuming functions in a React component. Let’s dive into the solution!

The Problem at Hand

Imagine you have a React component that performs extensive computations on large sets of data. Initially, an array in the component’s state tells the user that no computations are happening. However, once the computations begin, you want to update the state to reflect that those instances are either "Waiting ..." or "Done".

Here's a simplified version of your scenario:

You press a button to start the computation.

The state should show "Waiting ..." for each relevant element.

As the computations on each element conclude, the corresponding element's state should change to "Done".

But, as per your experience, using setTimeout inside the loop is not giving the desired updates in real-time.

The Solution

Using useState and useEffect:
We can leverage React's useState to manage our component's state, and useEffect to perform side effects when the state changes.

Setting Up the Component:
Incorporate a state variable to store your computations and another to track if the button has been pressed.

Creating the Time-Intensive Function:
Within a useEffect, we can start the time-intensive function after setting the state to show that the computations are underway.

Here is an example of how the code structure should look:

[[See Video to Reveal this Text or Code Snippet]]

Explanation of the Code

State Management:

state: Tracks the status of the computations (e.g., "No Computations", "Waiting ...", "Done").

isPressed: A flag to check if the button has been pressed.

Effect Hook:

The useEffect hook triggers the time-intensive function when the button is pressed, allowing us to perform required computations.

Timeout for Updates:

By using setTimeout, we update the specific index of the state to "Done" after each completion.

Conclusion

Managing long-running calculations can often be a hurdle in creating responsive user interfaces in React. By appropriately using useState and useEffect, along with strategic placement of setTimeout, you can effectively provide real-time feedback during extensive computations.

Now you can update the DOM elements while your heavy processing task runs so that users have a clear idea of the ongoing operations. Give it a try in your next React project!