JSFiddle - React, Tailwind, and code Playground

HTML

<label>Week:</label> <input type="number" id="week" value ="1" min="1" max="12"/>
<span id="student">N/A</span>

JavaScript

var students = ["Jeppe", "Tommy", "Rene", "Charlotte"];

function getStudentName(week) {
	var index = (week - 1) % students.length;
	return  students[index];
}

var weekInput = document.getElementById('week');
var output = document.getElementById('student');

weekInput.addEventListener('change', function() {
	output.innerHTML = getStudentName(this.value);
});