Run type type information loss about mfe-starter

[PatrickJS]

this is a browser thing where the type is probably a string so you would need to convert it via this._value = Number(newValue);. In TypeScript the types are removed when your code is compiled.

[dotcs]

Typescript is a typed superset of JavaScript that compiles to plain Javascript. In the example above Typescript assumes that newValue is a number. Whenever Typescript can check the type, it will do it for you. So Typescript would raise an error if you would try to do something like:

constructor() {
    this.onChange('abc');
}

onChange(newValue: number) {
    // ...
}

Unfortunately the component template is a string, which is only rendered at runtime. Because of this, Typescript does not now about your onChange call. Because Typescript compiles to plain Javascript, there is no way to do the type checking during runtime.

So yes, this is a problem. The only way to handle these kind of problems that I know is to do some additional type checking inside the function and be super careful about the arguments if Typescript can't do the proper checks for you.

To convert to a number you can always do

onChange(newValue: number) {
      console.log(+number * 3);
}

The unary plus operator enforces conversion to a number (see 4.14.2 The +, –, and ~ operators).

[PatrickJS]

@dotcs is correct in explaining how typescript works. if you need runtime type checks then you can check out this repo made by an angular core team member
https://github.com/vsavkin/RuntimeTypeChecks
If you have any more issues feel free to open another one or comment here