Typescript negative type check

Question

In typescript: is it possible to check if type expected type IS NOT some type? Or create an interface that defines methods/props that should not be there?

Answer 1

In typescript: is it possible to check if type expected type IS NOT some type?

I suspect what you are looking for is runtime types. TypeScript doesn't have a way to do this since there isn't a Standardized way to do this in JavaScript either.

If you are just looking for simple type guards they work fine e.g.

function foo(bar: string | number){
    if (typeof bar !== 'string') {
        // TypeScript knows its a number!
        return bar.toPrecision(3);
    }
}

More

Type guards : https://basarat.gitbooks.io/typescript/content/docs/types/typeGuard.html