JSFiddle - React, Tailwind, and code Playground

JavaScript

function primeAlert(n) {
  'use strict';
  var arr = [], m, p;
  for (m = 2; m <= n; m++) {
    p = 1;
    while (m % ++p);
    if (m === p) arr.push(m);
  }
  arr.forEach(alert);
  return '42';
}