rot13.js

const bigN = 13
			const alphas = 26
			const lowerCaseA = 'a'.charCodeAt(0)
			const upperCaseA = 'A'.charCodeAt(0)
			const rotate = str => str
				.normalize('NFD')
				.split('')
				.map(chr => chr.charCodeAt(0))
				.map(charCode =>
					(lowerCaseA <= charCode && charCode < lowerCaseA + alphas) ? ((charCode - lowerCaseA + bigN) % alphas) + lowerCaseA :
					(upperCaseA <= charCode && charCode < upperCaseA + alphas) ? ((charCode - upperCaseA + bigN) % alphas) + upperCaseA :
					charCode
				)
				.map(charCode => String.fromCharCode(charCode))
				.join('')

			const onChange = () => {
				const input = document.querySelector('.rot13__input')
				const output = document.querySelector('.rot13__output')
				output.value = rotate(input.value)
			}