Class members that are non-optional or are not unioned with undefined don't require initialisation. #20829

TypeScript Version: 2.6.2 strict mode

Apologies if this is a duplicate, I wasn't able to find a relevant issue.

Code

class Foo {
    test: number;
}

const foo = new Foo();

foo.test; //> undefined

Expected behavior:
I'd expect the code above to blow up, because I've not assigned a value to the test member. The compiler could require me to do either of the following to address the issue (similarly to how e.g. Java behaves):

1. Initialise in place:

class Foo {
    test: number = 42;
}

2. Initialise in the constructor:

class Foo {
    test: number;
    constructor() {
        this.test = 42;
    }
}

Actual behavior:
The above code compiles.