Typescript: Allows to mutate `const` with non-null assertion

[andy-ms]

TypeScript Version: 2.8.0-dev.20180209

Code

declare const x: number | undefined;
x!++;

Expected behavior:

src/a.ts(2,2): error TS2540: Cannot assign to 'x' because it is a constant or a read-only property.

Actual behavior:

No error.

[DanielRosenwasser]

But you said it was a constant?

[andy-ms]

The expected behavior is an error. The actual behavior is no error. For x: number and x++ there is correctly an error.

[DanielRosenwasser]

Sorry. It's been a long week.

[mhegazy]

thanks @jack-williams!

[jack-williams]

No problem!