javascript - Where can I make API call with hooks in react?

Question

Basically we do API calls in componentDidMount() life cycle method in React class components like below

     componentDidMount(){
          //Here we do API call and do setState accordingly
     }

But after hooks are introduced in React v16.7.0, its all like functional components mostly

My query is, where exactly do we need to make API call in functional component with hooks?

Do we have any method for it similar like componentDidMount()?

Answer 1

Yes, there's a similar (but not the same!) substitute for componentDidMount with hooks, and it's the useEffect hook.

The other answers don't really answer your question about where you can make API calls. You can make API calls by using useEffect and passing in an empty array or object as the second argument as a replacement for componentDidMount(). The key here is the second argument. If you don't provide an empty array or object as the second argument, the API call will be called on every render, and it effectively becomes a componentDidUpdate.

As mentioned in the docs:

Passing in an empty array [] of inputs tells React that your effect doesn’t depend on any values from the component, so that effect would run only on mount and clean up on unmount; it won’t run on updates.

Here are some examples for scenarios where you will need to make API calls:

API Call Strictly on Mount

Try running the code below and see the result.

function User() {
  const [firstName, setFirstName] = React.useState(null);
  const [lastName, setLastName] = React.useState(null);
  
  React.useEffect(() => {
    fetch('https://randomuser.me/api/')
      .then(results => results.json())
      .then(data => {
        const {name} = data.results[0];
        setFirstName(name.first);
        setLastName(name.last);
      });
  }, []); // <-- Have to pass in [] here!

  return (
    <div>
      Name: {!firstName || !lastName ? 'Loading...' : `${firstName} ${lastName}`}
    </div>
  );
}

ReactDOM.render(<User />, document.querySelector('#app'));

<script src="https://unpkg.com/[email protected]/umd/react.development.js"></script>
<script src="https://unpkg.com/[email protected]/umd/react-dom.development.js"></script>

<div id="app"></div>