log_js_errors.js

// logging function that will trap javascript errors and report them with a tracking pixel
// this obviously requires that you have access to your server logs. A tool like splunk comes in handy here.
var log_js_errors = {
  'pixel_path': '/track/event.gif',
  'is_loaded': false, // flag to let us know it's safe to log errors.
  'errors': [],
  'error_count': 0,
  'max_errors': 10, // prevent runaway logging for infinite loops
  'init': function() {
    // only render pixels after the dom is available
    var loaded = function() {  
      log_js_errors.is_loaded = true;   
      log_js_errors.report_errors();  
    };
    if (document.addEventListener) {
      window.addEventListener('load',loaded,false); 
    } else if  (document.attachEvent) {
      window.attachEvent("onload", loaded);
    }
    window.onerror = function(msg, url, line) { 
      log_js_errors.log_error(msg,url,line); return false; 
    };
  },
  'log_error': function(msg,url,line) {
  // save the errors to an array, this will be emptied out when the page is fully loaded.
    if (msg !== undefined && url !== undefined && this.error_count < this.max_errors) {
      this.error_count++;
      // build the url for the pixel
      var track_url = this.pixel_path;
      track_url += '?category=browser-errors&action='+escape(msg);
      track_url += '&jsurl='+escape(url);
      track_url += '&line='+escape(line);
      track_url += '&error_count='+this.error_count;
      track_url += '&t='+(new Date()).getTime();
      this.errors.push(track_url);
      // if it's safe to render the pixel, render it. Otherwise, wait a bit
      if (this.is_loaded == true) {
        this.report_errors();
      }
    }
  },
  'report_errors': function() {
    // loop through the errors array and render pixels for each one
    while(this.errors.length > 0) {
      var track_img = document.createElement('img');
      track_img.src = this.errors.shift();
      track_img.height = '1';
      track_img.width = '1';
      document.getElementsByTagName('body')[0].appendChild(track_img);
    }
  }
}
log_js_errors.init();