Variable with advanced type with optional property can be assigned simple type value

[hoegge]

TypeScript Version: TSLint 2.4.0 in VSCode and www.typescriplang.org playground today (2017-08-16)

Code

let a: { property?: string } = 1234; // why is this allowed?

Expected behavior:
It should not be possible to assign a number to a variable a of type { property?: string } or ... { property?: string | undefined; } if strict-null-check is turned on.

Actual behavior:
a is assigned the value 1234
If the type's property is not optional, it behaves as expected, i.e. type { property: string }.

[DanielRosenwasser]

Duplicate of #16333. Should be fixed in TypeScript 2.4.2.