How to use data outside useEffect?

In the variable const user inside useEffect function, I get an user object, I want to use the id, firstname and lastname from the user object in textfield. Is it somehow possible to use the user object outside the useEffect function?

In the code below the user object is undefined when used outside the useEffect.

Any help is appreciated!

import React, { useEffect, useState } from 'react';
import { useForm } from 'react-hook-form';
import { useLocation } from "react-router-dom";

interface userData {
    id: number;
    firstname: string;
    lastname: string;
};

const [obj, setObj] = useState();
const location = useLocation<userData>();
useEffect(() => {
    const user = allUsers.filter((obj) => obj.id === location.state.id);
    // handling if user is undefined
    if(user) {
        console.log('Storing object data')
        setObj(user);
    } else {
        console.log('No data!');
    }
}, [location]);

return (
        <div>
            <h1>User Data</h1>
            {/*Text field - id*/}
            <TextField
               name="id"
               id="id"
               label="ID"
               value={obj.id}
               fullWidth
             />
             {/*Text field - firstname*/}
             <TextField
               name="firstname"
               id="firstname"
               label="First Name"
               value={obj.firstname}
               fullWidth
             />
             {/*Text field - lastname*/}
             <TextField
               name="lastname"
               id="lastname"
               label="Last Name"
               value={obj.lastname}
               fullWidth
             />
        </div>
    );

Solution

In your code .filter() returns an array. Probably you want to use .find() instead. Also in either case I would update with setObj() your state because you can handle null in return also with obj && obj.id.

Try the following:

useEffect(() => {
    const user = allUsers.find((obj) => obj.id === location.state.id);
    setObj(user);
}, [location]);

Then in your return:

return <div>
   <h1>User Data</h1>
   {/* Showing TextField only if obj is not null */}
   { obj && <TextField name="id"
                       id="id"
                       label="ID"
                       value={obj.id}
                       fullWidth />}
</div>

I hope this clarifies!