I have the following situation. I am fetching data from the backend and the response is a bunch of objects. I want to iterate into them and in every iteration, I want to push them into my state.

here is how I am getting data from the backend:

     const allBookings = useSelector(getBookings);

      useEffect(() => {
        dispatch(
          fetchBookings.request({
            getAll: true,
          })
        );
      }, [dispatch]);

here is my data:

bookings:{
  0:{id: 294, address: '1585 Charleston Rd, Mountain View, CA, USA', broker:{name:'aaa'}},
  1:{id: 294, address: '1586 Charleston Rd, Mountain View, CA, USA', broker:{name:'bbb'}},
  2:{id: 294, address: '1587 Charleston Rd, Mountain View, CA, USA', broker:{name:'ccc'}}
}

Here where I am trying to set my data in an array, but something goes wrong, please help me to figure out how I can achieve. The final result should be like this:

    [
      {id: 294, address: '1585 Charleston Rd, Mountain View, CA, USA', broker:{name:'aaa'}},
      {id: 294, address: '1586 Charleston Rd, Mountain View, CA, USA', broker:{name:'bbb'}},
      {id: 294, address: '1587 Charleston Rd, Mountain View, CA, USA', broker:{name:'ccc'}}
    ]

     if (!allBookings) return null;

      const book = allBookings.bookings;
      const [books, setBooks] = useState([]);
      useEffect(() => {
        if (book) {
          const x = Object.entries(book);
          setBooks(x);
        }
      }, [book]);

    console.log('books===>', books);

here is my code in sandbox

I have the following situation. I am fetching data from the backend and the response is a bunch of objects. I want to iterate into them and in every iteration, I want to push them into my state.

here is how I am getting data from the backend:

     const allBookings = useSelector(getBookings);

      useEffect(() => {
        dispatch(
          fetchBookings.request({
            getAll: true,
          })
        );
      }, [dispatch]);

here is my data:

bookings:{
  0:{id: 294, address: '1585 Charleston Rd, Mountain View, CA, USA', broker:{name:'aaa'}},
  1:{id: 294, address: '1586 Charleston Rd, Mountain View, CA, USA', broker:{name:'bbb'}},
  2:{id: 294, address: '1587 Charleston Rd, Mountain View, CA, USA', broker:{name:'ccc'}}
}

Here where I am trying to set my data in an array, but something goes wrong, please help me to figure out how I can achieve. The final result should be like this:

    [
      {id: 294, address: '1585 Charleston Rd, Mountain View, CA, USA', broker:{name:'aaa'}},
      {id: 294, address: '1586 Charleston Rd, Mountain View, CA, USA', broker:{name:'bbb'}},
      {id: 294, address: '1587 Charleston Rd, Mountain View, CA, USA', broker:{name:'ccc'}}
    ]

     if (!allBookings) return null;

      const book = allBookings.bookings;
      const [books, setBooks] = useState([]);
      useEffect(() => {
        if (book) {
          const x = Object.entries(book);
          setBooks(x);
        }
      }, [book]);

    console.log('books===>', books);

here is my code in sandbox

• javascript
• reactjs

• Since you already have allBookings why add the same entries in local state ? You can use the allBookings directly. Additionally you cannot use hooks conditionally, meaning that you cannot have a branch like if (..) return null; and then add a useXXX hook after that line. – Gabriele Petrioli Commented Dec 28, 2021 at 9:09

5 Answers 5

Use functional update to push new entires into your books array:

const x = Object.entries(book);
setBooks(books => [...books, ...x]);

Since you’re always instantiating with an empty array you also don’t need the falsy check, ie you can remove if (books).

change const x = Object.entries(book); to const x = Object.values(book);

In your useEffect use the store selector var to watch changes ,

also you shouldn't use Object.entries in your case , instead use Object.values ,

Object.entries will get both key and values , and put them as an array for each entry like

[["0",{id: 294, address: '1585 Charleston Rd,...}]]

but Object.values wil only create new array from values ( your objects )

your code should looks like

  const [books, setBooks] = useState([]);
  useEffect(() => {
    if (allBookings.bookings) {
      const entries = Object.values(allBookings.bookings);
      setBooks(entries);
    }
  }, [allBookings]);

Try the below Snippet :

// Get a hook function
const {useState, useEffect } = React;

const Example = ({title}) => {
   let serverObject = {
    bookings:{
      0:{id: 294, address: '1585 Charleston Rd, Mountain View, CA, USA', broker:{name:'aaa'}},
      1:{id: 294, address: '1586 Charleston Rd, Mountain View, CA, USA', broker:{name:'bbb'}},
      2:{id: 294, address: '1587 Charleston Rd, Mountain View, CA, USA', broker:{name:'ccc'}}
    }
  }
  
  const [allBookings, setAllBookings] = useState({});
  
  const [books, setBooks] = useState([]);
  
  setTimeout(()=> { setAllBookings(serverObject)},  2000)
  
  
  useEffect(() => {
    if (allBookings.bookings) {
      const entries = Object.values(allBookings.bookings);
      setBooks(entries);
    }
  }, [allBookings]);
  
  return (
    <div>
      {
         books.map( book => <p> {book.address} </p>)
      }
    </div>
  );
};

// Render it
ReactDOM.render(
  <Example title="Example using Hooks:" />,
  document.getElementById("app")
);

<script src="https://cdnjs.cloudflare./ajax/libs/react/17.0.1/umd/react.production.min.js"></script>
<script src="https://cdnjs.cloudflare./ajax/libs/react-dom/17.0.1/umd/react-dom.production.min.js"></script>
<div id="react"></div>

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

use Object.values instead of Object.entries.

Also, merge new res with the previous res.

const data = Object.entries(book);
setBooks(books => [...books, ...data]);

Never remended to mutate the state directly.

The remended approach in later React versions is to use an updater function when modifying states to prevent race conditions:

For Functional Components

const [array,setArray] = useState([]);

Push value at the end:

setArray(oldArray => [...oldArray,newValue] );

Push value at the beginning:

setArray(oldArray => [newValue,...oldArray] );

For Class Components

Push string to end of the array, you do this...

this.setState(prevState => ({
  myArray: [...prevState.myArray, "new value"]
}))

Push string to beginning of the array, you do it like this ...

this.setState(prevState => ({
  myArray: ["new value", ...prevState.myArray]
}))

Push object to end of the array, you do this ...

this.setState(prevState => ({
  myArray: [...prevState.myArray, {"name": "object"}]
}))

Push object to beginning of the array, you do this ....

this.setState(prevState => ({
  myArray: [ {"name": "object"}, ...prevState.myArray]
}))