For example we have a ‘useState‘ function, which takes a state and a function to update the state:
const useState = (state, setState) => { const newState = setState(state); if (newState != null) { return newState; } else { return state; } };
If the new state is not undefined or null, we will return newState otherwise, we return the original state.
But when we run the code like this:
const res = useState([1], state => state.push(2)); // 2
We expect the res to be [1, 2], but we got 2, this is because ‘push‘ method return the length of the array as a result.
To solve the problem we can use ‘void‘ keyword, it will execute the expression and return undefined as a result, for example:
void 2 == ‘2‘ // (void 2) == ‘2‘, the same as undefined == ‘2‘, which is false void (2 == ‘2‘) // void false which is undefined
const useState = (state, setState) => { const newState = setState(state); if (newState != null) { return newState; } else { return state; } }; const res = useState([1], state => void state.push(2)); console.log(res); //[1,2]
[Javascript] Avoid Accidental Returns of New State by using the void Keyword
原文：https://www.cnblogs.com/Answer1215/p/11688327.html