Why is my javascript function being printed as undefined?

Question

I'm new to JavaScript and am currently learning about functions. Whenever I try to print this to the console, it is being returned as undefined. I'm sure its something super simple, but what am I missing? Here is my code:

let getSleepHours = day => {
  switch (day) {
    case 'monday':
      return 8;
      break;
    case 'tuesday':
      return 7;
      break;
    case 'wednesday':
      return 6;
      break;
    case 'thursday':
      return 9;
      break;
    case 'friday':
      return 10;
      break;
    case 'saturday':
      return 8;
      break;
    case 'sunday':
      return 11;
      break;
    default:
      return 'error';
  }
}
const getActualSleepHours = () => {
  return
  getSleepHours('monday') +
    getSleepHours('tuesday') +
    getSleepHours('wednesday') +
    getSleepHours('thursday') +
    getSleepHours('friday') +
    getSleepHours('saturday') +
    getSleepHours('sunday');
};
console.log(getActualSleepHours());

In a `switch` you use either a `return` or a `break` but not both. — Scott Marcus, Feb 20 '20 at 22:37
const getActualSleepHours = () => getSleepHours('monday') + getSleepHours('tuesday') +..... + getSleepHours('sunday'); — epascarello, Feb 20 '20 at 22:48

score 2 · Answer 1 · edited Feb 20 '20 at 22:41

it returns undefined because of this line

const getActualSleepHours=()=>{ return

here there is nothing returned after return keyword, so Javascript will consider its undefined.

you should do this:

const getActualSleepHours =() =>{ 
  return getSleepHours('monday')+
  getSleepHours('tuesday')+
  getSleepHours('wednesday')+
  getSleepHours('thursday')+
  getSleepHours('friday')+
  getSleepHours('saturday')+
  getSleepHours('sunday');

};

Full snippet:

let getSleepHours = day => {
  switch (day) {
    case 'monday':
      return 8;
      break;
    case 'tuesday':
      return 7;
      break;
    case 'wednesday':
      return 6;
      break;
    case 'thursday':
      return 9;
      break;
    case 'friday':
      return 10;
      break;
    case 'saturday':
      return 8;
      break;
    case 'sunday':
      return 11;
      break;
    default:
      return 'error';
  }
}
const getActualSleepHours =() =>{ 
  return getSleepHours('monday')+
  getSleepHours('tuesday')+
  getSleepHours('wednesday')+
  getSleepHours('thursday')+
  getSleepHours('friday')+
  getSleepHours('saturday')+
  getSleepHours('sunday');

};
console.log(getActualSleepHours());

KooiInc · Answer 2 · 2020-02-22T12:03:49.613

You have your answer. Just for fun: your code can be simplified a little. Now it's thursday over here, so I'm going to get my 9 hours sleep :P

// just use an object
const getSleepHours = {
  monday: 8,
  tuesday: 7,
  wednesday: 6,
  thursday: 9,
  friday: 10,
  saturday: 8,
  sunday: 11
};
// and create the string using a template string
// btw without brackets in the arrow function
// there's no need for 'return'
const getActualSleepHours = () =>
  `${getSleepHours.monday} ${
     getSleepHours.tuesday} ${
     getSleepHours.wednesday} ${
     getSleepHours.thursday} ${
     getSleepHours.friday} ${
     getSleepHours.saturday} ${
     getSleepHours.sunday}`;

console.log(getActualSleepHours());

// or, as noted in comments, even easier
console.log(Object.values(getSleepHours).join(` `));

.as-console-wrapper { top: 0; max-height: 100% !important; }

const getActualSleepHours = () => Object.values(getSleepHours).join(' ') — Josh Wulf, Feb 22 '20 at 11:58

score 1 · Answer 3 · answered Feb 20 '20 at 23:13

I know this wasn't your question, but while you are learning JS, consider refactoring this imperative snippet as a data structure:

const getSleepHours = day => {
  const hours = {
    'monday': 8,
    'tuesday': 7,
    'wednesday': 6,
    'thursday': 9,
    'friday': 10,
    'saturday': 8,
    'sunday': 11
   }
   return hours[day] || 'error';
}

Whenever you find yourself writing repetitive code, it is usually a sign that there is a data structure in your program that you are creating manually.

Why is my javascript function being printed as undefined?

3 Answers3