Typescript: Type 'number | null' is not assignable to type 'number'

Question

I have the following code:

let statistics = this.video.getStatistics();

let currentLikeCount : number = statistics!.getLikeCount() ? statistics.getLikeCount() : 1;

However, I get the following error when compiling with Typescript

error TS2322: Type 'number | null' is not assignable to type 'number'.

My conditional checks to see if the like count is null, and, if so, assigns it to a number, but typescript still complains about it possibly being null.

How to I properly assign the like count to a number?

Answer 1

There's no way for TypeScript to know that getLikeCount() returns the same value every time it's called. There are lots of other ways to write this code in a way that doesn't invoke the function twice, e.g.:

statistics.getLikeCount() || 1

Or

const c = statistics.getLikeCount();
let c2 = c == null ? c : 1;

Answer 2

Just for some clarification why the compiler still complains:

if you write the ternary statement as if/else, you get

if (statistics!.getLikeCount()) {
    currentLikeCount = statistics.getLikeCount();
} else {
    currentLikeCount = 1;
}

The TS Compiler evaluates the two calls to getLikeCount() independently and thus complains about possible null values. Ryan's answer provides possible ways to get around this.