打字稿中的联合类型？

Question

为什么TypeScript中不允许这种类型的定义？

type profileType = 'TEACHER' | 'PRINCIPAL';

interface FormList {
    [ key: profileType ] : IForm[];
}

let forms: FormList;

forms = {
    'TEACHER' : [{ id: 1, name: "o" }, { id: 1, name: "b" }]
}

它将在以下行中引发错误：[ key: profileType ] : IForm[];。

Answer 1

您可以将字符串文字从并集映射为新类型。这在打字稿中称为mapped type：

type IForm = {};
type ProfileType = 'TEACHER' | 'PRINCIPAL';    

type FormList = { [P in ProfileType]: IForm[] };

let forms: FormList;

forms = {
    'TEACHER': [{ id: 1, name: "o" }, { id: 1, name: "b" }],
    'PRINCIPAL': [{ id: 1, name: "o" }, { id: 1, name: "b" }]
}