converting 12 to 24 hours

timeConversion12to24hrs.js

const isAm = (s = '', regex = /am/) => regex.test(s.toLowerCase())
const getHead = (s = '') => s.split(':')[0]
const getTail = (s = '') => s.slice(2, 8)
const convertToNum = (s = '') => parseInt(s)
const convertedNum = (s = '') => convertToNum(getHead(s))
const calcAm = (s = '') =>
	convertedNum(s) === 12
		? (convertedNum(s) - 12).toString() + 0
		: convertedNum(s) < 10
		? '0' + convertedNum(s)
		: convertedNum(s)
const calcPm = (s = '') =>
	convertedNum(s) === 12 ? 24 - convertedNum(s) : convertedNum(s) + 12
const calcAmOrPm = (s = '') => (isAm(s) ? calcAm(s) : calcPm(s))

function timeConversion(s) {
	const tail = getTail(s)
	const time = calcAmOrPm(s) + tail
	return time
}

const s = '01:00:00PM'
timeConversion(s) // 13:00:00