const labelTypeMap = useMemo<Record<'between' | 'inner', string>>(
() => ({
between: formatMessage({ id: 'addGroup' }),
inner: '+',
aaa: 123, // no error here
}),
[]
);
作为代码，没有错误aaa，即使它与useMemo的返回类型不匹配。任何帮助都感激不尽。
useMemo 返回类型错误，但是tsc 不会显示错误？
IT技术
reactjs
typescript
react-hooks
2021-05-26 15:02:20
1个回答
这是一个仍然可以证明问题的简化版本：
const labelTypeMap: Record<"between" | "inner", string> = (() => ({
between: "xxx",
inner: "+",
aaa: 123,
}))();
问题是 Typescript 通常允许对象具有额外的属性。毕竟，有额外的属性的对象是与所述基类型兼容（在一个面向对象的意义上）。只有当您使用Object.keys类似的动态内省功能时才会出现惊喜。
这种灵活性的唯一例外是当您尝试直接分配对象文字时：
const labelTypeMap: Record<"between" | "inner", string> = {
between: "xxx",
inner: "+",
aaa: 123, // Error as expected
};
现在它会按预期抱怨。
因此，您的问题的一种可能解决方案是：
const labelTypeMap = useMemo(() => {
const result: Record<"between" | "inner", string> = {
between: "xxx",
inner: "+",
aaa: 123, // Error as expected
};
return result;
}, []);
这也有效：
const labelTypeMap = useMemo(
(): Record<"between" | "inner", string> => ({
between: "xxx",
inner: "+",
aaa: 123, // Error as expected
}),
[],
);