Struggling with object type casting in Typescript

Question

Struggling with object type casting in Typescript

Having issues with casting objects from an HTTP API response to Typescript.

I am trying to cast the json data to a Typescript object using the "as" keyword or <Type >, but it's not working as expected.

r.forEach(entry => {
    entry.creationDate = new Date(entry.creationDate.date);
    entry.creator = <User>entry.creator;
    return entry;
});

The console.log after casting the entry.creator still shows "Object".

Any advice on how to properly cast objects in this scenario?

angular typescript types

Answer 1

Answer №1

I have encountered similar issues in the past, and in my perspective, this is a flaw in typescript. When performing the cast as demonstrated or with code like the example below:

class User {
    name: string;

    doConsole(): void {
        console.log(`Name: ${this.name}`);
    }
}

let userObj = { name: 'jose' };

let user = new User();
Object.assign(user, userObj);

user.doConsole();

You may observe that the doConsole function will not be accessible in the casted object. This is how the resulting JS code looks after compilation:

var User = (function () {
    function User(name) {
        this.name = name;
    }
    User.prototype.doConsole = function () {
        console.log("Name: " + this.name);
    };
    return User;
}());
var userObj = { name: 'jose' };
var user = userObj;
user.doConsole();

It becomes evident that the prototype function from the class is not utilized when casting. In my experience, a workaround would involve something along these lines:

class User {
    name: string;

    doConsole(): void {
       console.log(`Name: ${this.name}`);
    }
}

let userObj = { name: 'jose' };

let user = new User();
Object.assign(user, userObj);

user.doConsole();

This approach ensures that the proper prototype function is employed, as seen in the compiled JS code:

var User = (function () {
    function User() {
    }
    User.prototype.doConsole = function () {
        console.log("Name: " + this.name);
    };
    return User;
}());
var userObj = { name: 'jose' };
var user = new User();
Object.assign(user, userObj);
user.doConsole();

In essence, my standpoint aligns with yours - it should function as intended, but due to the limitation of the transpiler, it doesn't utilize the prototyped function properly.

I trust this explanation aids you in understanding the issue better.

Answer 2

I have encountered similar issues in the past, and in my perspective, this is a flaw in typescript. When performing the cast as demonstrated or with code like the example below:

class User {
    name: string;

    doConsole(): void {
        console.log(`Name: ${this.name}`);
    }
}

let userObj = { name: 'jose' };

let user = new User();
Object.assign(user, userObj);

user.doConsole();

You may observe that the doConsole function will not be accessible in the casted object. This is how the resulting JS code looks after compilation:

var User = (function () {
    function User(name) {
        this.name = name;
    }
    User.prototype.doConsole = function () {
        console.log("Name: " + this.name);
    };
    return User;
}());
var userObj = { name: 'jose' };
var user = userObj;
user.doConsole();

It becomes evident that the prototype function from the class is not utilized when casting. In my experience, a workaround would involve something along these lines:

class User {
    name: string;

    doConsole(): void {
       console.log(`Name: ${this.name}`);
    }
}

let userObj = { name: 'jose' };

let user = new User();
Object.assign(user, userObj);

user.doConsole();

This approach ensures that the proper prototype function is employed, as seen in the compiled JS code:

var User = (function () {
    function User() {
    }
    User.prototype.doConsole = function () {
        console.log("Name: " + this.name);
    };
    return User;
}());
var userObj = { name: 'jose' };
var user = new User();
Object.assign(user, userObj);
user.doConsole();

In essence, my standpoint aligns with yours - it should function as intended, but due to the limitation of the transpiler, it doesn't utilize the prototyped function properly.

I trust this explanation aids you in understanding the issue better.

Answer 3

Answer №2

While Javascript itself does not inherently support strong typings, Typescript can be used to implement strong typing at compile-time. It is important to note that any unexpected behavior during runtime is actually the expected behavior and not a flaw in your code.

Typescript offers a variety of useful features including:

Compile time checking: Identify potential errors in your code before they impact your users.

Strongly-typed objects: Specify the type of objects your functions expect to minimize unforeseen outcomes.

You can find more information about the benefits of strong typing and Typescript here.

Answer 4

While Javascript itself does not inherently support strong typings, Typescript can be used to implement strong typing at compile-time. It is important to note that any unexpected behavior during runtime is actually the expected behavior and not a flaw in your code.

Typescript offers a variety of useful features including:

Compile time checking: Identify potential errors in your code before they impact your users.

Strongly-typed objects: Specify the type of objects your functions expect to minimize unforeseen outcomes.

You can find more information about the benefits of strong typing and Typescript here.

Struggling with object type casting in Typescript

Answer №1

Answer №2

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