Implement strict mode

[andreas-aeschlimann]

Today, I have learned about some new (~1-2 year old) compiler options of TypeScript which help to write better code and prevent errors. That is why I suggest that we implement this flag (called strict mode) in this library and also in all Angular/TypeScript projects that we have.

From the documentation:

Enable all strict type checking options.
Enabling --strict enables --noImplicitAny, --noImplicitThis, --alwaysStrict, --strictBindCallApply, --strictNullChecks, --strictFunctionTypes and --strictPropertyInitialization.

Source: https://www.typescriptlang.org/docs/handbook/compiler-options.html

To summarize: The compiler option strict enables seven flags that help you write better code. It is possible that in future releases more flags will be added.

As of now, we only have two flags set in this library: noImplicitAny and strictNullChecks. I suggest we remove those two flags from tsconfig.json and replace it with strict: true.

[tobiasschweizer]

Thanks for this, I will move it to youtrack.

Btw: I ordered new book about TypeScript that should cover this too :-)

[andreas-aeschlimann]

The strict flag forbids you to do things like that:

export class User {
    name: string;
}

Then:

const user = new User();
console.log(user.name); // undefined even though we told the compiler it should be string

I have dicussed implications of this issue with @tobiasschweizer on the phone lately. Basically, as of now, you can define such a User class which never assigns a name. It basically means that name can be undefined and it should be flagged as such.

With the strict flags, developers are forced to write name: string | undefined or assign a value in the constructor.

[tobiasschweizer]

I think the flag you are talking about is strictPropertyInitialization .

[andreas-aeschlimann]

Yes, but strict is a superset of that and thus better. Microsoft/Typescript states that in future they may add more flags that will be still covered if strict is set to true.