Recently I added a few ads to WhoShouldiFollow to cover our hosting costs and ran into a Javascript issue I hadn’t hit before. Specifically, trying to dynamically load a third party script that uses document.write to add HTML to the DOM was erasing the whole page! I found a (slightly-evil) solution after much hacking around and no luck finding anything similar in Google. Hopefully there is a cleaner solution out there, but thought I’d write up my fix.

The way that the ad network supplies the ad is for publishers to include a short snippet like this:

<script src="" type="text/javascript"></script>

Within the ad javascript it does something like this (simplified for this example):

document.write("Click on this ad!");

Nice and simple to drop in to HTML, but our results page is built dynamically from an AJAX call that fetches JSON. At first I thought I could just built a new script tag and append it to the div I wanted, but that resulted in a blank page with just the ad in the DOM. I’m assuming that without an enclosing context that the document.write is overwriting the root html node.

Instead what worked was to temporarily override document.write just before the ad is loaded and write the content of the ad into the DOM where I wanted. This works, but feels a bit evil. I’d be interested in finding a prettier solution than this.

var original_write = document.write;

// Re-assign doc.write while the ad is loaded.
document.write = function(ad_html) {
  // Append the contents of the ad to a special div.

  // restore original write
  document.write = original_write; 
// Create a script element in the DOM to load the ad.
var e = document.createElement("script");
e.src = "";