不允许 null 或未定义的 useState 和 TypeScript？

Question

I'm adding TypeScript types to React's useState hook.

const [checked, setChecked] = React.useState<"checked" | un-checked">(null);

Is it possible to only allow the checked and un-checked values and not null or undefined so that the code above would error?

Answer 1

You need to enable "strictNullChecks": true in your tsconfig.json

Argument of type 'null' is not assignable to parameter of type '"checked" | "un-checked" | (() => "checked" | "un-checked")'.

https://www.typescriptlang.org/docs/handbook/release-notes/typescript-2-0.html