Greeting Functions "Good morning, Good afternoon and Good evening"

Question

Today I came across a very interesting topic, which are the greetings "Good morning, Good afternoon and Good night" in Javascript (and among other languages..)

Where in failed attempt to create a simple, small and easy code too "hit me" with some eventualities. Follow the code below:

var h = new Date('May 31, 2021 09:00:00').getHours(); // alterna entre 06, 12, 18, 00
var greetings = ['Boa madrugada', 'Bom dia', 'Boa tarde', 'Boa noite'];

console.log(greetings[h / 6]); // dividindo a hora por 6, seu resultado servirá para encontrar a posição do valor na Array

It had everything to work, but the values of the current hours, between the 6 and 12 (7, 8, 9, ...), the 12 and 18 (13, 14, 15, ...) and the 18 and 00 (19, 20, 21, ...).

The values between them consequently are not found in Array the result of the division by 6 of the current time, unless the Array had their respective values according to the result.

amid:

• 06 and 12 = Good morning
• 12 and 18 = Good afternoon
• 18 and 00 = Good evening
• 00 and 05 = Good morning

---

Applying ..

I arrived at this result that somehow "cleaned up" the problem!

const greetingMessage = () => {
  let h = new Date().toLocaleTimeString('pt-BR', {hour: 'numeric', hour12: false}); // formato 24 horas (0-23)
  if (h >= 0 && h <= 5) { // entre meia noite (0h) e 5 da madrugada
    return 'Boa madrugada';
  } else if (h >= 6 && h < 12) { // entre 6 e 11 da manhã
    return 'Bom dia';
  } else if (h >= 12 && h < 18) { // entre meio dia (12h) e 17 (5h) da tarde
    return 'Boa tarde';
  } else if (h >= 18 && h <= 23) { // entre 18 (6h) e 23 (11h) da noite
    return 'Boa noite';
  }
}

console.log(greetingMessage());

but would have somehow more "clean" without requiring the use of so many Ifs/Else?

^{Obs: the intention is to leave the code with fewer lines possible!}

Answer 1

Edit:

As reported in the comment of hkotsubo informing that it facilitates the adoption of the Date.prototype.getHours() which returns the time to the specified date, according to the local time.
So lines:

let h = new Date().toLocaleTimeString('pt-BR', { 
   hour: 'numeric',
   hour12: false 
});

Were replaced by:

let h = new Date().getHours();

Some possible refactoring for your code:

• Using conditional statement if.

const greetingMessage = () => {
  //let h = new Date().toLocaleTimeString('pt-BR', { hour: 'numeric', hour12: false });
  let h = new Date().getHours();
  if (h <= 5) return 'Boa madrugada';
  if (h < 12) return 'Bom dia';
  if (h < 18) return 'Boa tarde';
  return 'Boa noite';
}

console.log(greetingMessage());

• Using the conditional statement switch/case.

const greetingMessage = () => {
  //let h = new Date().toLocaleTimeString('pt-BR', { hour: 'numeric', hour12: false }); 
  let h = new Date().getHours();
  switch (true) {
    case h <= 5: return 'Boa madrugada';
    case h < 12: return 'Bom dia';
    case h < 18: return 'Boa tarde';
    default: return 'Boa noite';
  }      
}

console.log(greetingMessage());

• Using the operator ternary parole.

const greetingMessage = () => {
  //let h = new Date().toLocaleTimeString('pt-BR', { hour: 'numeric', hour12: false });
  let h = new Date().getHours();
  return (h <= 5) ? 'Boa madrugada' :
         (h < 12) ? 'Bom dia' :
         (h < 18) ? 'Boa tarde' :
         'Boa noite';
}

console.log(greetingMessage());

• Using mathematics.

const greetingMessage = () => {
  var greetings = ['Boa madrugada', 'Bom dia', 'Boa tarde', 'Boa noite'];
  //let h = new Date().toLocaleTimeString('pt-BR', { hour: 'numeric', hour12: false });
  let h = new Date().getHours();
  return greetings[(h / 6) >> 0];   //Trunca o resultado da divisão obtendo sempre um inteiro.
}

console.log(greetingMessage());