JSFiddle - React, Tailwind, and code Playground

TypeScript

const foo = (x: number) => {
    console.log("foo")
    return x * x;
}

const isXUndefined = (x?: number) => x === undefined;

const boo = (x?: number) => {
    if (isXUndefined(x)) {
        return 0;
    }

    return foo(x!);
}

console.log(boo(1))