Fisher-Yates shuffle algorithm to randomly select elements to show/hide.

randomlyShowElements.js

window.addEventListener('DOMContentLoaded', function() {
  var elements = document.querySelectorAll('.changing');
  var numOfElements = elements.length;
  var numOfElementsToShow = 5;
  
  if (numOfElements <= numOfElementsToShow) {
    for (var i = 0; i < numOfElements; i++) {
      elements[i].style.display = 'block';
    }
    return;
  }
  
  // Shuffle the array of elements using the Fisher-Yates algorithm
  for (var i = numOfElements - 1; i > 0; i--) {
    var j = Math.floor(Math.random() * (i + 1));
    var temp = elements[i];
    elements[i] = elements[j];
    elements[j] = temp;
  }
  
  // Show the first numOfElementsToShow elements in the shuffled array
  for (var i = 0; i < numOfElementsToShow; i++) {
    elements[i].style.display = 'block';
  }
});