Why is my checkbox not updating on click?

Question

I'm trying to build a form where users will have to check mapped checkboxes, but every time I click on a checkbox nothing happens. The idea would be that every times user checks the box its value is added to an array. But when I log e.target.checked I just see true every times I click on the checkbox, never false. Also the checkbox doesn't check on a click. Does anyone know where this problem can come from?

This is my code:

const [arr, setArr] = useState([])

const handleCheck = e => {
    if (e.target.checked) {
        setArr([e.target.value, ...arr])
    } else {
        setArr(arr.filter(value => value !== e.target.value))
    }
}

And JSX:

{results.map(person => (
    <li key={uuid()}>
        <input
            type="checkbox"
            id={`user-${person._id}`}
            value={person._id}
            onChange={handleCheck}
            name="name"
        />
        
        {person.fullName}
    </li>
))}

Thanks for your help!

Does this answer your question? [Push method in React Hooks (useState)?](https://stackoverflow.com/questions/54676966/push-method-in-react-hooks-usestate) — codemonkey, Dec 23 '21 at 22:37

score 0 · Accepted Answer · answered Dec 23 '21 at 23:12

You are generating random React keys each render cycle, so the uncontrolled inputs effectively reset each time. Use the person._id as the React key so you've stable references identifying the list items and inputs.

{results.map((person) => (
  <li key={person._id}>
    <input
      type="checkbox"
      id={`user-${person._id}`}
      value={person._id}
      onChange={handleCheck}
      name="name"
    />
    {person.fullName}
  </li>
))}

Why is my checkbox not updating on click?

1 Answers1