JSFiddle - React, Tailwind, and code Playground

JavaScript

function gen4Numbers() {
    var numbers = [];
    while (numbers.length < 4) {
        var newNr = (parseInt(Math.random() * 4))+1;
        if (numbers.indexOf(newNr) == -1) {
            numbers.push(newNr);
        }
    }
    return numbers;
}
alert(gen4Numbers());