Why Does useEffect Run on Initial Render in React?

How to Prevent the useEffect Hook from Running on Initial Render

The React documentation states that the componentDidUpdate() lifecycle method is not invoked during the initial render. However, when using the useEffect hook to simulate componentDidUpdate(), it appears to run on every render, including the first one.

Explanation

The useEffect hook runs after every render cycle, including the initial one. Unlike the componentDidUpdate() method, it does not have a built-in check to skip the first run.

Solution

There are two approaches to address this:

1. Using useRef

We can use the useRef hook to track whether it's the first time the useEffect function is being called.

const isFirstRender = useRef(true);

useEffect(() => {
  if (isFirstRender.current) {
    isFirstRender.current = false;
    return; // Skip the first render
  }

  console.log("Component did update");
}, [<dependencies>]);

2. Using useLayoutEffect

useLayoutEffect is similar to useEffect, but it runs in the same phase as componentDidUpdate(), which occurs after DOM operations.

useLayoutEffect(() => {
  console.log("Component did update");
}, [<dependencies>]);

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