从 object 中删除密钥并更新无状态组件

Question

 const [description, setDescription] = React.useState({
   "key1":"first value",
   "key2":"second value",
   "key3":"third value"
 }
)

I have an object like the one provided above. i tried deleting a key from the object with the function below.

const remove = (key) => {
   delete description[key]
}

the problem i am having is, when i call this function the key is deleted form the object, but react does not update the state.

Answer 1

Note that you're mutating a local instance of your state. You should update the state through the useState hook.

const remove = (key) => {
   setDescription(description => ({
     ...description,
     [key]: undefined
   }))
}

Note that you should never mutate your state. This can cause bugs in your application, So in the code above, we make a new object, copy the data we have, and then just set [key] to undefined, effectively deleting the value there.

Answer 2

the problem i am having is, when i call this function the key is deleted form the object, but react does not update the state.

That is because you should not mutate state. Using delete description[key] will mutate the state, and doesn't inform React that a re-render should be triggered.

You should use setDescription to inform React about a state change. And instead of mutating the existing state, create a new one without the key property. This can easily be done with destructuring assignment .

const remove = (key) => {
  setDescription(({ [key]: value, ...description }) => description);
};

In the solution above we extract the value of the key property and store it in the value variable. All other properties (without key ) are collected in a new object and stored in the description variable.

This process essentially creates a copy of the old description without the key property and uses it as the new state.

---

If you pass remove as a property to other components you could consider usinguseCallback as well. This stabilises the identity of the remove function and could result in less re-renders.

const remove = useCallback((key) => {
  setDescription(({ [key]: value, ...description }) => description);
}, []);

Normally you pass your dependencies in the dependency array at the end, but because the identity of setDescription is stable you can omit this dependency.

If all the dependencies have a stable identity or the dependency array is empty, the resulting function has a stable identity as well.