Convert minutes portion of time to decimal

Question

I am making an hours calculator app. It takes a start time, end time and time taken for lunch.

For the start and end time it takes a four-digit hh:mm time. For example: 10:20.

I have made a function which converts the time into a decimal, so 10:20 = 10.33. The function works, but I feel it looks a little heavy and wondered if anyone has any suggestions of how I could make it better...

const minuteConverter = time => {
    let h = Number(time.split(':')[0]);
    let m = Math.round((1 / 60 * (Number(time.split(':')[1])) + Number.EPSILON) * 100) / 100;
    let mConverted = Number(m.toString().split('.')[1])
    return Number(`${h}.${mConverted}`)
};
console.log(minuteConverter('10:20'))

The time must be output as a number to two decimal places. For example,

• '10:20' >> 10.33
• '9:45' >> 9.75
• '15:33' >> 15.55

Answer 1

• Use const instead of let to declare variables if the value doesn't change.

• You are executing time.split(':') twice.

• A short method to convert a string to a number is the unary +.

• JavaScript has the toFixed() method to format a number to a fixed number of digits:

---

function minuteConverter(time) {
   const [h, m] = time.split(':');
   const value = +h + +m / 60;
   return value.toFixed(2);
}

Answer 2

Simpler technique

Per answers to this identical question from six years ago on stack overflow the formula for converting the minutes doesn’t need to be so complex. Many of the answers there use parseInt() to parse numbers from the strings but the unary plus operator + can be used instead for faster operation and simpler syntax (refer to answers to parseInt vs unary plus, when to use which? for more context).

The minutes can be divided by sixty and added to the number of hours to create a Number. The method Number.toFixed() can be used to limit floating point numbers to a specified number of digits.

ES-6 Variable declarations

Because ES6 keywords like let are used array destructuring can be used to assign the values for h and m in one expression which avoids extra calls to the split() method. This allows for const to be used, which is a good habit to help avoid accidental re-assignment.

Extra terminator after arrow function block

A multi-line arrow function expression does not require a semi-colon after the body but it doesn't hurt to have one at the end- especially if you are not familiar with the rules of Automatic semicolon insertion.

Simplified code

Here is one way it could be simplified.

const minuteConverter = time => {
    const [h, m] = time.split(':');
    return (+h + (+m/60)).toFixed(2);
};
['9:45', '10:03', '10:20', '15:33'].forEach(
    time => console.log(time, ' >> ', minuteConverter(time))
)

Answer 3

Better is relative! Lots of ways to write that code.

Though I personally prefer terse and precise code like other answers have highlighted, (here is my take on that):

const minuteConverter = time => [time.split(':')]
  .map(([hour, minute]) => +(+hour + +minute / 60).toFixed(2))[0]

The pluses could get a little hectic so here is a more descriptive/arithmetic dense version as well.

const minuteConverter = time => [time.split(':')]
  .map(([hh, mm]) => [+hh, mm / 60])
  .reduce((hundred, [hours, minutes]) => Math.round((hours + minutes) * hundred) / hundred, 100)

Answer 4

Use + instead of Number() on ES6.

Use const instead of let or var if the value for this variable not going to change.

Use a deconstructing assignment to create variables from the array let [h,m] = time.split(/[.:]/).

This will accept 10:30 or 10.30, also in case the time is .30 will add 0 for hours variable.

const timeStringToFloatMm = time => {
  let [h,m] = time.split(/[.:]/);
        h = h || 0;
  return (+h + +m / 60).toFixed(2);
}