[object] Cast object to interface in TypeScript

I'm trying to make a cast in my code from the body of a request in express (using body-parser middleware) to an interface, but it's not enforcing type safety.

This is my interface:

export interface IToDoDto {
  description: string;
  status: boolean;
};

This is the code where I'm trying to do the cast:

@Post()
addToDo(@Response() res, @Request() req) {
  const toDo: IToDoDto = <IToDoDto> req.body; // <<< cast here
  this.toDoService.addToDo(toDo);
  return res.status(HttpStatus.CREATED).end();
}

And finally, the service method that's being called:

public addToDo(toDo: IToDoDto): void {
  toDo.id = this.idCounter;
  this.todos.push(toDo);
  this.idCounter++;
}

I can pass whatever arguments, even ones that don't come close to matching the interface definition, and this code will work fine. I would expect, if the cast from response body to interface is not possible, that an exception would be thrown at runtime like Java or C#.

I have read that in TypeScript casting doesn't exist, only Type Assertion, so it will only tell the compiler that an object is of type x, so... Am I wrong? What's the right way to enforce and ensure type safety?

Here's another way to force a type-cast even between incompatible types and interfaces where TS compiler normally complains:

export function forceCast<T>(input: any): T {

  // ... do runtime checks here

  // @ts-ignore <-- forces TS compiler to compile this as-is
  return input;
}

Then you can use it to force cast objects to a certain type:

import { forceCast } from './forceCast';

const randomObject: any = {};
const typedObject = forceCast<IToDoDto>(randomObject);

Note that I left out the part you are supposed to do runtime checks before casting for the sake of reducing complexity. What I do in my project is compiling all my .d.ts interface files into JSON schemas and using ajv to validate in runtime.

If it helps anyone, I was having an issue where I wanted to treat an object as another type with a similar interface. I attempted the following:

Didn't pass linting

const x = new Obj(a as b);

The linter was complaining that a was missing properties that existed on b. In other words, a had some properties and methods of b, but not all. To work around this, I followed VS Code's suggestion:

Passed linting and testing

const x = new Obj(a as unknown as b);

Note that if your code attempts to call one of the properties that exists on type b that is not implemented on type a, you should realize a runtime fault.