Display greeting by time via TS

index.js

"use strict";
const greeting = () => {
    const day = new Date();
    const hour = day.getHours();
    let result = null;
    if (hour >= 5 && hour < 12) {
        result = "Good morning";
    }
    else {
        if (hour >= 12 && hour < 18) {
            result = "Good afternoon";
        }
        else {
            if (hour >= 18 && hour < 24) {
                result = "Good evening";
            }
            else {
                if (hour >= 0 && hour < 5) {
                    result = "Good night";
                }
            }
        }
    }
    return result;
};
console.log(greeting());

index.ts

type Greeting = () => string | null;
type Result = string | null;

const greeting: Greeting = () => {
    const day: Date = new Date();
    const hour: number = day.getHours();

    let result: Result = null;

    if (hour >= 5 && hour < 12) {
        result = "Good morning";
    } else {
        if (hour >= 12 && hour < 18) {
            result = "Good afternoon";
        } else {
            if (hour >= 18 && hour < 24) {
                result = "Good evening";
            } else {
                if (hour >= 0 && hour < 5) {
                    result = "Good night";
                }
            }
        }
    }

    return result;
}

console.log(greeting());