Check if variable is a specific interface type in a typescript union

Question

Is it possible to create a typeguard, or something else that accomplishes the same purpose, to check if a variable is a specific interface type in a typescript union?

Answer 1

Since Typescript 1.6 you can use user-defined type guards:

let isFoo = (object: Foo| Bar): object is Foo => {
    return "a" in object;
}

See https://www.typescriptlang.org/docs/handbook/advanced-types.html#user-defined-type-guards and https://github.com/microsoft/TypeScript/issues/10485