React: How to use setState inside functional component?

Question

I am learning React. I read an article that suggests us to use functional component instead of class that extends React.Component, so I followed. I also use the arrow function instead of function keyword. That is:

const MyComponent = (props) => {...}

I got a structure that has 20 properties like:

{
    id: '',
    firstname: '',
    lastname: '', 
    ...
}

I am using if ... else if ... to set the state, but I saw some examples that use this.setState() in just one line of code. I try to import setState from 'react', but fail.

Is there a way to use setState() instead of setName(), setId(), ..., etc? Or any suggestion?

Thank you very much!

Answer 1

There is only the (one) 'setState()' method - not a method per-property (as you've suggested/questioned).

It is a composite in terms of it's parameter, in that you can specify/set more than one item within the same/one call (to the 'setState()' method), so you can set all 20 of your items in one go.

E.g.

  this.setState({ "firstName" : firstNameVal, "lastName" : lastNameVal });

I was starting from where you said you started - from a 'class' based component.

If you are sticking with the switch to a 'function' based component, then it is slightly different, in summary:

import React, { useState } from 'react';

...

// The 'useState' hook (function) returns a getter (variable) & setter (function) for your state value - and takes the initial/default value for it/to set it to, e.g.
const [ firstName, setFirstName ] = useState('');

And you then use the getter var to read it & the setter function to set it:

  setFirstName('Dennis');

(I could be wrong but I believe 'hooks' were added in v16.8 of React.)

A more in-depth description:

https://www.simplilearn.com/tutorials/reactjs-tutorial/reactjs-state#:~:text=1%20A%20state%20can%20be%20modified%20based%20on,merge%20between%20the%20new%20and%20the%20previous%20state

Answer 2

Use useState hook in functional components.

const App = () => {
  const [state, setState] = React.useState({ first: "hello", second: "world" });
  
  return (
    <div>
      <input type="text" value={state.first} onChange={(ev) => setState({...state, first: ev.target.value})} />
      <input type="text" value={state.second} onChange={(ev) => setState({...state, second: ev.target.value})} />
    </div>
  )


}


ReactDOM.render(<App />, document.getElementById('app'))

<script crossorigin src="https://unpkg.com/react@17/umd/react.production.min.js"></script>
<script crossorigin src="https://unpkg.com/react-dom@17/umd/react-dom.production.min.js"></script>

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