Front End Performance and Today’s Typical Web Sites

In order to understand how the front end, especially JavaScript, is impacting web performance today, some typical web pages were studied. The following table shows content composition of the front pages of two representative web sites, American Airline (www.aa.com) and FaceBook (www.facebook.com):

Table 1: Content Composition of Selected Web Sites

In both cases, the initial HTML text is only a small percentage of the page footprint (23% and 3% respectively). This is generally true for web pages today. Secondly, the biggest portion of both pages is JavaScript, at 42% and 77% respectively. It is not uncommon to find web sites today that JavaScript comprises 40% to 90% of the footprint.

Further, various researches concluded that the front end is where majority of the page loading time is spent for today’s web pages. For example, Yahoo’s Web Performance team studied some major web sites’ front page loading time as shown in table 2. The result show that, in average, only 5% to 20% of the page loading time is caused by server processing and network transfer of the initial HTML content while up to 90% of page loading time is spent processing the content: (Reference 2: http://yuiblog.com/blog/2006/11/28/performance-research-part-1/):

As a result, Yahoo team concluded a “performance golden rule” in reference 3: optimize front-end performance first, that’s where 80% or more of the end-user response time is spent.

In summary, for today’s web pages:

• The server time for generating HTML content and network transfer time for such content are only small factors in page performance, typically only 5% to 20% of the page loading time.


• Front end processing time can be as high as 95% of page loading time.


• HTML is only a small portion of the footprint while JavaScript can be a significant portion of the footprint, sometimes as high as 80% to 90%;


• JavaScript code performance can be the major performance influencer.