React Performance Optimization: Avoiding Unnecessary Re-renders with Refs

• Refs (useRef hook): A mechanism in React to directly access DOM elements or store mutable values that don't trigger re-renders.
• useEffect hook: Manages side effects in functional components, like data fetching, subscriptions, or DOM manipulation.

The Issue with ref.current in useEffect's Dependency Array

• Refs themselves are mutable: Their values can change over time.
• useEffect's dependency array controls re-runs: If a dependency changes, the effect runs again.
• Including ref directly in the array can lead to infinite loops: Each re-run due to the ref change might cause another re-run if the ref updates within the effect.

Reasons to Avoid It

• Unexpected Behavior: The infinite loop scenario can make your component behave erratically.
• Performance Issues: Unnecessary re-runs can slow down your application.

Recommended Approaches

1. Extract the Value from ref.current:

   • If you need the DOM element's value within the effect, extract it from ref.current on the first render and use that value in the dependency array. This ensures the effect only runs when the extracted value changes.

   const myRef = useRef(null);
   
   useEffect(() => {
       const element = myRef.current;
       // Use element here (only runs when element changes)
   }, [element]);
   

2. Create a Custom Hook (Advanced):

When It Might Be Okay (Use with Caution)

• Simple Effects: In very specific cases with a single, simple effect that directly modifies the DOM element pointed to by the ref, it might work. However, it's generally better to avoid this due to potential maintainability issues and the risk of unintended behavior.

Key Points

• Refs are for direct DOM access and mutable value storage, not for triggering re-renders.
• Use the extracted value or a custom hook for useEffect dependencies based on ref values.
• Be cautious about using ref.current directly in the dependency array.

import React, { useRef, useEffect } from 'react';

function MyComponent() {
  const myRef = useRef(null);

  // Extract the element on the first render and use it in the dependency array
  useEffect(() => {
    const element = myRef.current;

    if (element) {
      // Do something with the element here (e.g., focus)
      element.focus();
    }
  }, [element]); // Only runs when `element` (extracted value) changes

  return (
    <div ref={myRef}>This is my element</div>
  );
}

In this example, useEffect only runs once on the initial render (when element is first assigned) or when the element itself changes (e.g., when the component re-renders due to other state or prop changes).

Avoiding ref.current in Dependency Array (Simpler Case):

import React, { useRef } from 'react';

function MyComponent() {
  const myRef = useRef(null);

  // No dependency array needed, focus happens on initial render
  useEffect(() => {
    if (myRef.current) {
      myRef.current.focus();
    }
  });

  return (
    <div ref={myRef}>This is my element</div>
  );
}

This is a simpler case where you only need to focus the element once on the initial render. Since the effect doesn't rely on any changing values, you can omit the dependency array altogether.

• Callback refs allow you to get notified when a ref is attached or detached from a DOM element.
• This can be useful for triggering side effects when the element becomes available or disappears.

import React, { useEffect } from 'react';

function MyComponent() {
  const [hasElement, setHasElement] = useState(false);

  const setRef = (element) => {
    setHasElement(element !== null); // Update state when element changes
  };

  useEffect(() => {
    if (hasElement) {
      // Do something with the element here
      console.log(element);
    }
  }, [hasElement]); // Only runs when `hasElement` changes

  return (
    <div ref={setRef}>This is my element</div>
  );
}

In this example, the setRef function updates the hasElement state when the ref is attached or detached. The useEffect then runs only when hasElement changes, ensuring the effect only executes when the element is available.

Layout Effect (Use with Caution):

React provides a less common hook called useLayoutEffect. Unlike useEffect, it runs synchronously after DOM mutations. This can be useful in specific cases where you need to read layout information from the DOM and immediately re-render based on that information.

Important Note: Use useLayoutEffect sparingly as it can cause performance issues if used excessively.

For complex scenarios involving multiple refs or intricate logic, consider creating a custom hook that encapsulates the ref and effect logic. This can improve code organization and maintainability. The custom hook can manage dependencies internally based on the ref values.

Choosing the Right Method:

• For simple cases: Use the approach of extracting the value from ref.current or avoiding the dependency array entirely (if only needed on initial render).
• For scenarios where you need to react to element attachment/detachment: Use callback refs.
• For specific cases requiring immediate DOM layout information: Use useLayoutEffect with caution.
• For complex ref and effect logic: Consider creating a custom hook.