我在哪里可以使用钩子进行 API 调用？

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/react@16.7.0-alpha.0/umd/react.development.js"></script> <script src="https://unpkg.com/react-dom@16.7.0-alpha.0/umd/react-dom.development.js"></script> <div id="app"></div>

API Call Whenever Some Prop/State Changes

If you are for example displaying a profile page of a user where each page has a userID state/prop, you should pass in that ID as a value into the second parameter of useEffect so that the data will be refetched for a new user ID. componentDidMount is insufficient here as the component might not need remounting if you go directly from user A to user B's profile.

In the traditional classes way, you would do:

componentDidMount() {
  this.fetchData();
}

componentDidUpdate(prevProps, prevState) {
  if (prevState.id !== this.state.id) {
    this.fetchData();
  }
}

With hooks, that would be:

useEffect(() => {
  this.fetchData();
}, [id]);

Try running the code below and see the result. Change the id to 2 for instance to see that useEffect is run again.

 function Todo() { const [todo, setTodo] = React.useState(null); const [id, setId] = React.useState(1); React.useEffect(() => { if (id == null || id === '') { return; } fetch(`https://jsonplaceholder.typicode.com/todos/${id}`) .then(results => results.json()) .then(data => { setTodo(data); }); }, [id]); // useEffect will trigger whenever id is different. return ( <div> <input value={id} onChange={e => setId(e.target.value)}/> <br/> <pre>{JSON.stringify(todo, null, 2)}</pre> </div> ); } ReactDOM.render(<Todo />, document.querySelector('#app'));

 <script src="https://unpkg.com/react@16.8.1/umd/react.development.js"></script> <script src="https://unpkg.com/react-dom@16.8.1/umd/react-dom.development.js"></script> <div id="app"></div>

You should read up on useEffect so that you know what you can/cannot do with it.

Suspense

As Dan Abramov said on this GitHub Issue :

Longer term we'll discourage this (useEffect) pattern because it encourages race conditions. Such as — anything could happen between your call starts and ends, and you could have gotten new props. Instead, we'll recommend Suspense for data fetching

So stay tuned for Suspense!

Answer 2

You can use a library that provides the hooks for you like https://resthooks.io

Then getting your data becomes as simple as:

const article = useSuspense(ArticleResource.detail(), { id });

Now you grabbed the article by id. All non-happy paths (loading, error states) are handled by Suspense and Error boundaries respectively.

To get started follow this simple guide: https://resthooks.io/docs/getting-started/installation

At only 7kb gzipped this will save you a lot of pain and in the long run lower your bundle size due to less repeated code.

Demos

Answer 3

I am just posting this as a simpler way to understand acc. to my efforts. Credit to Yangshun Tay's post that it covers almost everything.

API call on mounting of component

Code:

  useEffect(() => { 
    // here is where you make API call(s) or any side effects
    fetchData('/data')
  }, [] ) /** passing empty brackets is necessary */

So using useEffect(fn,[]) with empty args as [] makes fn() triggered once throughout when component creates(mounts) and destroys(unmounts) without depending on any values.

Pro tip:

Also further if you return() something in this fn then it will act same as componentWillUnmount() lifecycle as that of class component.

  useEffect(() => { 
   fetchData('/data')
   return () => {
    // this will be performed when component will unmount
    resetData()
   }
  }, [] )

API call when some value changes

If you are looking to call API when some value changes, simply pass that variable (which is storing value) into arguments array in useEffect() .

 useEffect(() => {
  // perform your API call here
  updateDetails();
 },[prop.name]) /** --> will be triggered whenever value of prop.name changes */

This will make sure that whenever value of prop.name changes, your function in hook gets triggered.

Also to note : this hook will be also called initially when the component is mounted. So at that time your name value might be in initial state which is kind of unintended from your view. So you can add custom condition in your function to avoid unnecessary API calls.

Answer 4

When you are using functional components with the hooks API, you can use the useEffect() method to produce side effects. Whenever the state is updated because of these side effects, the component will re-render.

Example from the docs.

import { useState, useEffect } from 'react';

function Example() {
  const [count, setCount] = useState(0);

  // Similar to componentDidMount and componentDidUpdate:
  useEffect(() => {
    // Update the document title using the browser API
    document.title = `You clicked ${count} times`;
  });

  return (
    <div>
      <p>You clicked {count} times</p>
      <button onClick={() => setCount(count + 1)}>
        Click me
      </button>
    </div>
  );
}

For example, you could call setCount in a callback function of an async request. When the callback is executed, the state will get updated and React will re-render the component. Also from the docs:

Tip

If you're familiar with React class lifecycle methods, you can think of useEffect Hook as componentDidMount , componentDidUpdate , and componentWillUnmount combined.

Answer 5

You could also use use-http like:

import useFetch from 'use-http'

function App() {
  // add whatever other options you would add to `fetch` such as headers
  const options = {
    method: 'POST',
    body: {}, // whatever data you want to send
  }

  var [data, loading, error] = useFetch('https://example.com', options)

  // want to use object destructuring? You can do that too
  var { data, loading, error } = useFetch('https://example.com', options)

  if (error) {
    return 'Error!'
  }

  if (loading) {
    return 'Loading!'
  }

  return (
    <code>
      <pre>{data}</pre>
    </code>
  )
}