Chapter 1, Becoming Functional – Several Questions

1.1 TypeScript, please! The following are the fully annotated versions of the code in the chapter. This is the code for the factorial functions:

// question_01_typescript_please.ts
function fact(n: number): number {
  if (n === 0) {
    return 1;
  } else {
    return n * fact(n - 1);
  }
}
const fact2 = (n: number): number => {
  if (n === 0) {
    return 1;
  } else {
    return n * fact2(n - 1);
  }
};
const fact3 = (n: number): number =>
  n === 0 ? 1 : n * fact3(n - 1);

This is the code for the spreading examples:

// continued...
function sum3(a: number, b: number, c: number): number {
  return a + b + c;
}
const x: [number, number, number] = [1, 2, 3];
const y = sum3(...x); // equivalent to sum3(1,2,3)
const f = [1, 2, 3];
const g = [4, ...f, 5];...