Collection of useful TS Snippets

ts-tricks.ts

// Inclusive overlap of two types
type CommonProperties<T, U> = {
    [K in keyof T & keyof U]: T[K] extends U[K] ? U[K] extends T[K] ? T[K] : never : never;
};

// Function signature that varies second arg type based on type of first
type Args<T> = T extends number ? Foo : T extends string ? Bar : never;

function dependentFunction<T extends number | string>(arg1: T, arg2: Args<T>): void {
    if (typeof arg1 === "number") {
        console.log("Number and Foo", arg1, (arg2 as Foo).fooProp);
    } else if (typeof arg1 === "string") {
        console.log("String and Bar", arg1, (arg2 as Bar).barProp);
    }
}