Extend interface to contain a date type

问题

I need to extend an interface in Typescript to contain a Date type.

I have tried the following

interface WithDate {
  [key: string]: Date;
}

But when I try to extend WithDate, I get the error:

interface Person extends  WithDate {
  id: number; // Property 'id' of type 'number' is not assignable to string index type 'Date'
  name: string;
  date: Date;
}

Any ideas how to fix this error? Many thanks

回答1:

interface WithDate {
  [key: string]: Date;
}

With this interface you are telling TypeScript that objects implementing this interface can have string keys but only Date values.

const obj: IWithDate = {
  key1: new Date(), // OK because it's a date
  key2: new Date('2020-01-01') // OK, another date
  key3: '2020-01-01' // Error, not a Date
  key4: true // Error, not a Date
  key5: 123 // Error, not a Date 
  // and any other objects besides `Date`s will cause a compiler error
}

So when you extend the WithDate interface, TypeScript sees the index signature and attempts to merge these interfaces, however, there are conflicting shapes here:

{ id: string }

and

{ [k: string]: Date }

So the compiler tries its best to solve these conflicts and because this is a fairly ambiguous situation, TypeScript has to choose some a shape and it chooses { [k: string]: Date } because this is the most expected/correct behaviour for interface extensions.

You probably intended to do this:

interface WithDate {
 date: Date
}

interface Person extends WithDate {
 id: number;
 name: string;
}

const person: Person = {
 id: 1,
 date: new Date(),
 name: 'bob'
}

回答2:

Name the field in WithDate:

interface WithDate {
  date: Date; // Note field name : date
}
interface Person extends  WithDate {
  id: number;
  name: string;
}

来源：https://stackoverflow.com/questions/63071377/extend-interface-to-contain-a-date-type

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typescript

types

interface

extends