When examined, the dates within a Typescript interface are essentially strings

Regrettably, presenting the entire code to replicate this issue would be quite lengthy, so I am hoping that the problem is apparent based on the provided information. If necessary, I can supply a more comprehensive solution.

Initially, I define an interface:

export interface ITest {
myDate: Date;
}

Subsequently, I generate an array of these interfaces for testing purposes:

export const TEST: ITest[]=[{myDate: new Date(1995, 8, 1)}]

I expose these through an Angular2 service that interacts with the InMemoryDbService from angular2-in-memory-web-api. The section of code where I make the call and retrieve the array appears as follows:

get(): Promise<ITest[]>{
return this.http.get(this.testUrl)
.toPromise()
.then(response => response.json().data as ITest[])
.catch(this.handleError);
}

...and then I bring it into my component using:

    this.testService.get().then(tests => {
this.tests = tests;
console.log("Date Type:"+typeof(this.tests[0].myDate));
});

Everything functions correctly, however, the issue arises when the console.log statement displays:

Date Type:string

The data itself is accurate, with the string representing my date being 1995-09-01T07:00:00.000Z, but the primary concern is - rather than a Date, it registers as a string! Even though VS Code provides auto-completion for methods like toDateString, executing them results in toDateString is not a function.

I suspect the problem lies within

response => response.json().data as ITest[]
, but why isn't the date data being converted into an actual Date? Clearly, there is a mistake in my approach. How should I address this matter to ensure that my objects conform to the expected types?

Answer №1

When working with an interface and utilizing type assertion in TypeScript, you are essentially informing the language that the object adheres to that specific interface.

However, it is crucial to note that what you are casting is a JSON object where the "myDate" property appears as a string.

It's important to understand that using type-assertion will not impact the generated JavaScript code at all - you must handle the actual type conversion manually.

The reason behind the "myDate" property being represented as a string is due to the lack of a defined Date type in JSON format. Therefore, the server likely sends the result of date.toString().

An approach you could take is creating a class to represent the returned value and then instantiate an object from the JSON properties like this:

var response = JSON.parse(JSON.stringify({ myDate: new Date() }));

class Test  {
    constructor(json: { myDate: string }) {

        this.myDate = new Date(json.myDate);
    }

    myDate: Date;
}

let test = new Test(response);
console.log("Type: " + typeof (test.myDate));
console.log("Value: " + test.myDate);

Answer №2

When I work with dates in angular, I follow these steps:

  1. First, I define the date property in my interface User.ts like this:

    export interface User { id?: string; date?: any; }

  2. Next, in my component file (ts file), I initialize the date property like so:

    date = new Date();

This line of code sets the date to the current date.

  1. After that, I assign a value to the date property using the toDate() method like this:

    this.date = this.outputDate.toDate()

  2. Finally, I display the date in my template file (html) as usual.

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