React Hooks: useState()

What are React Hooks?
They are functions in React that allow you to add react functionality to function based components.

What is the useState hook?
The useState hook is used to add state to a function-based component. The syntax will follow a common pattern:

const [listEntry, setListEntry] = useState('');

• listEntry is the state variable.

• setListEntry is the function used to edit the state variable. Note, you should only edit the state variable through this function.

• useState('') is setting the initial value of the state variable. In this case, when listEntry is initialized, it equals an empty string.

This example lets you enter a value, then add it to a bulleted list:

import { useState } from 'react';

const App = () => {
  const [listEntry, setListEntry] = useState('');
  const [listEntries, setListEntries] = useState([]);

  const handleInputChange = (e) => {
    setListEntry(e.target.value);
  };

  const handleAddButtonClick = () => {
    setListEntries((listEntries) => [...listEntries, listEntry]);
    setListEntry('');
  };

  return (
    <div>
      <input type='text' value={listEntry} onChange={handleInputChange} />
      <button onClick={handleAddButtonClick}>Add</button>
      <ul>
        {listEntries.map((entry) => {
          return <li>{entry}</li>;
        })}
      </ul>
    </div>
  );
};

• const [listEntries, setListEntries] = useState([]); we are creating a value listEntries and initially setting it as an empty array. This will hold our list items.

• <input type="text" value={listEntry} onChange={handleInputChange} /> each time you enter a character in this input, the listEntry variable is being updated to what you are typing.

• <button onClick={handleAddButtonClick}>Add</button> when clicked, the value of listEntry is being appended to the listEntries array.

• {listEntries.map((entry) => {return <li>{entry}</li>;})} the values in listEntries are being rendered in a bulleted list.

More information can be found in Reacts official documentation: https://reactjs.org/docs/hooks-state.html