Typescript: `strictPropertyInitialization` should allow private initialization helpers

Created on 1 Jul 2019 · 2Comments · Source: microsoft/TypeScript

Search Terms

strictPropertyInitialization
class initialization helper

Suggestion

It's a common pattern to delegate class initialization to helper methods to reduce the size of the constructor. This makes it more maintainable. However, when using --strictNullChecks and --strictPropertyInitialization, TypeScript complains because it's unable to infer the initialization since it's in a helper function. The argument in https://github.com/microsoft/TypeScript/issues/21132 is that it's because of inheritance, but I think it should work if the helper method is marked a private (or private class field #), since a subclass would not be able to access it.

Not only is it annoying to have to do private foo!: string;, but it's also hard to know to do that, so most just end up either removing the helper methods or using // @ts-ignore. It's also TS's goal to support common JS pattern as best as possible.

Use Cases

Explained above.

Examples

class A {
    private foo: string; // <== TypeScript complains

    constructor() {
        this.initStuff();
    }

    private initStuff() {
        this.foo = 'foo';
    }
}

Checklist

My suggestion meets these guidelines:

[x] This wouldn't be a breaking change in existing TypeScript/JavaScript code
[x] This wouldn't change the runtime behavior of existing JavaScript code
[x] This could be implemented without emitting different JS based on the types of the expressions
[x] This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, etc.)
[x] This feature would agree with the rest of TypeScript's Design Goals.

In Discussion Suggestion

Source