How JavaScript Tags Affect Site Performance

By Justin Bougher

December 20, 2018


When it comes to the overall performance of a website there is one reliable constant: visitors want speed. Research shows that visitor behavior is directly related to browsing speed and that conversion rates and overall customer satisfaction drop when pages load slowly. So, when you implement an A/B testing solution that uses JavaScript tags to create page variations, you put your site and A/B testing program into a catch-22. You lose data accuracy because of misfires, you lose visitors because of the poor user experience, and you have to choose between a slow site or a site with flicker. This blog will break down why your site may experience latency issues, and how to A/B test while maintaining site speed and avoiding latency altogether.

Synchronous Versus Asynchronous Tags

Most page load time occurs in the browser, where JavaScript code is a key factor. JavaScript tags then have the greatest effect on site speed. However, not all tags influence speed to the same degree, and tags that change content carry greater weight and affect site speed the most.

Content-swapping tags, the type used by many optimization vendors, come in two common variations: synchronous and asynchronous tags.

Synchronous tags:

  • Effectively block all content below them from loading until the tag returns content.
  • Load slower while retrieving content.

Asynchronous tags:

  • Continue to load the remainder of the webpage while the browser retrieves content.
  • Produce flicker while retrieving and loading the new A/B test version.

How To Improve Site Speed

The only way to A/B test and optimize your digital channels without incurring latency (and so also rendering your data unreliable) is to avoid content-swapping JavaScript tags.

SiteSpect uses a non-intrusive, tagless architecture that is entirely different from any other solution in the testing and targeting space. SiteSpect’s Find and Replace technology makes content changes on request, rather than at rendering. This method allows more power and flexibility, does not require any page tagging, and thus sidesteps an array of performance issues.

Checkout the ebook, “Speed Feeds Business: How JavaScript Tags Affect Performance,” for more information, including data on the impact latency has on conversions and revenue, and more ways to avoid the problem.

To learn more about SiteSpect, visit our website.


Justin Bougher

Justin Bougher

Justin Bougher was the VP of Product at SiteSpect.

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