How to fix missing dependency warning when using useEffect React Hook?

Question

With React 16.8.6 (it was good on previous version 16.8.3), I get this error when I attempt to prevent an infinite loop on a fetch request

./src/components/Bu         


        

Answer 1

./src/components/BusinessesList.js
Line 51:  React Hook useEffect has a missing dependency: 'fetchBusinesses'.
Either include it or remove the dependency array  react-hooks/exhaustive-deps

It's not JS/React error but eslint (eslint-plugin-react-hooks) warning.

It's telling you that hook depends on function fetchBusinesses, so you should pass it as dependency.

useEffect(() => {
  fetchBusinesses();
}, [fetchBusinesses]);

It could result in invoking function every render if function is declared in component like:

const Component = () => {
  /*...*/

  //new function declaration every render
  const fetchBusinesses = () => {
    fetch('/api/businesses/')
      .then(...)
  }

  useEffect(() => {
    fetchBusinesses();
  }, [fetchBusinesses]);

  /*...*/
}

because every time function is redeclared with new reference

Correct way of doing this stuff is:

const Component = () => {
  /*...*/

  // keep function reference
  const fetchBusinesses = useCallback(() => {
    fetch('/api/businesses/')
      .then(...)
  }, [/* additional dependencies */]) 

  useEffect(() => {
    fetchBusinesses();
  }, [fetchBusinesses]);

  /*...*/
}

or just defining function in useEffect

More: https://github.com/facebook/react/issues/14920