如何为createMessage
方法强制使用正确的第二个参数类型
const EMAIL_TEMPLATES = {
DOCTOR_SIGNUP: DoctorSignupOutput,
CHANGE_PASSWORD: PasswordParams
} as const;
@Injectable()
export class EmailService {
sendEmail() {
console.log('Email sent!');
}
createMessage(template: keyof typeof EMAIL_TEMPLATES, params: ?) {
}
}
所以当模板等于DoctorSignupOutput
时,只允许类型为DOCTOR_SIGNUP
的对象吗?
答案 0 :(得分:6)
那样尝试
createMessage<
T extends keyof typeof EMAIL_TEMPLATES, // <- T points to a key
R extends (typeof EMAIL_TEMPLATES)[T] // <- R points to the type of that key
>(template: T, params: R) {
}
详细示例:
interface MyInterface {
keyString: string;
keyNumber: number;
}
function createMessage<
O extends object, // object itself
K extends keyof O, // all its keys
V extends O[K] // types of keys, once K is specified, it's narrowed to related type.
>(object: O, key: K, value: V) {
console.log(object, key, value);
}
const data: MyInterface = {
keyString: 'hello',
keyNumber: 777,
};
createMessage(data, 'keyString', 'world'); // works
createMessage(data, 'keyNumber', 42); // works
createMessage(data, 'keyString', 42); // fails due to wrong type
createMessage(data, 'keyNumber', 'world'); // fails due to wrong type
createMessage(data, 'keyUnknown', 'random'); // fails due to missed key in the original interface.