In Angular 2 templates using Typescript, there is flexibility with type enforcement in the code, allowing for a more

I have been following this particular tutorial

Check out the code snippet below

HTML

<li *ngFor="let hero of heroes" (click)="onSelect(hero.id)">
  <span class="badge">{{hero.id}}</span> {{hero.name}} 
</li>

TS file

selectedHero: Hero;

onSelect(hero: Hero): void {
  console.log(hero); // outputs 11 
  console.log(typeof hero); // outputs number
  this.selectedHero = hero;
}

The onSelect method expects a parameter of type Hero, but surprisingly, no errors are shown if a different type is passed in. Even assigning a number to this.selectedHero does not cause an error.

Does this mean that template types are not strictly enforced?

I would appreciate it if someone could point out what I am missing here.

Thank you

Answer №1

While TypeScript can catch compile-time errors, it does not have the ability to control or validate the execution of code during runtime.

Answer №2

The absence of types in JavaScript is the reason why no errors are being reported by the browser. TypeScript, on the other hand, verifies types prior to translating the code into plain JavaScript.

Answer №3

When working on the html file for this assignment, errors may not be visible. However, if you mistakenly place the code inside a TypeScript file like this:

constructor(){
  this.onSelect(1); //<-- this will give you an error that the method is expecting a Hero type but that you've given a number
}

You will encounter errors.

To answer your question: "Is template types simply not enforced?"; They are not.

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