update squarespace instructions to handle ajax loading

Author: twhiteaker

squarespace.md

@@ -38,6 +38,36 @@ search features, you can delete those elements from the HTML.
 </script>
 ```
 
+3. If your Squarespace template has AJAX loading enabled (most modern ones do),
+   then you'll have to change the `window.onload` portion of pasta.js to use
+   `Squarespace.onInitialize` instead.  Since that function can fire when you
+   navigate away from the data search page, it can throw errors that would be
+   visible in your browser console since your other pages don't have the same
+   elements as your data search page. To get around that, you can have the
+   pasta.js code only execute when a specific element id is found on the page,
+   such as the search form which has an id of `dataSearchForm`.  The code edits
+   look like the example below.
+
+```js
+// We're toward the end of the pasta.js code here
+// We commented out the window.onload function to replace it
+// window.onload = function () {
+window.Squarespace.onInitialize(Y, function() {
+   // This snippet prevents this code from running on other pages
+   var searchEl = document.getElementById("dataSearchForm");
+   if (!searchEl)
+      return;
+
+   // Rest of code that was in the onload function goes here
+   function initApp(expanded) {
+   // ...snip...
+
+// The last line of the file was a close braket for the onload function.
+// For Squarespace.onInitialize, we need a bracket AND a paren.
+// };  // commented out the ending for onload
+});  // New ending which fits Squarespace.onInitialize
+```
+
 ## Task 4. Add CSS
 
 The style rules for the application need to be added under custom CSS for the