打字稿：如何根据同一接口内的布尔值排除可选性？

Question

I have an interface and I am trying to implement this:

export interface Passenger {
       id: number,
       name: string,
       checkedIn: boolean,
       checkedInDate?: Date // <- How to make this optional only if checkedIn = false
}

Answer 1

why dont you just ignore the value of variable checkedInDate when checkedIn is true , something like this

if(!pessageobj.checkedIn) {
 pessageobj.checkedInDate = new Date();
} else {
pessageobj.checkedInDate =  some default date like min date;
}

Answer 2

You can't declare this in an interface. However you could implement this behaviour in a class:

export class Passenger {
   id: number;
   name: string;
   checkedInDate?: Date;

   get checkedIn() {
      return this.checkedInDate != null;
  }       
 }

Answer 3

You can define Union Type :

export type Passenger = {
    id: number,
    name: string,
    checkedIn: true,
    checkedInDate: Date
} | {
    id: number,
    name: string,
    checkedIn: false
    checkedInDate?: Date // you can just this field
}

Answer 4

A template parameter can specify the type of checkedIn with greater specificity (than just boolean ). An intersection can then "add" either the optional or required version of checkedInDate .

export type Passenger<A extends boolean> = {
    id: number;
    name: string;
    checkedIn: A;
} & (A extends false
    ? {
        checkedInDate?: Date;
    }
    : {
        checkedInDate: Date;
    });