randomise_order.js

// $(document).ready() replacement.
function ready(fn) {
  if (document.readyState != 'loading'){
    fn();
  } else {
    document.addEventListener('DOMContentLoaded', fn);
  }
}

// Randomise a set of items with the following structure:
// <div class="items"><div>Item 1</div><div>Item 2</div><div>Item 3 etc</div></div>
// Uses localStorage to save the order.
ready(function () {
  var items = document.querySelector('.items');
  var storedOrder = JSON.parse(localStorage.getItem("storedOrder"));

  if (items) {
  // If order has been saved in localStorage.
    if (storedOrder) {
      for (i = items.children.length; i > 0; i--) {
        var index = i - 1;
        items.appendChild(items.children[storedOrder[index]]);
      };
    } else {
      // Order has not been saved, generate new random order and save.
      var storedOrder = [];
      for (i = items.children.length; i > 0; i--) {
        var order = Math.floor(Math.random() * i);
        storedOrder.push(order);
        items.appendChild(items.children[order]);
      };
      localStorage.setItem("storedOrder", JSON.stringify(storedOrder));
    }
  }
});