Browser monitoring's JavaScript snippet introduces a nearly invisible impact on website performance and user perception of the time it takes a page to load. The JavaScript is included in a packet of webpage data that is sent anyway. In addition, it immediately begins monitoring for errors and events as the rest of the webpage executes. The negligible amount of overhead required to load the JavaScript results in a significant return of actionable data.
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Overall impact
The JavaScript's overhead takes into consideration both the impact on the user and the impact on your systems' performance:
- User perception: Typically users cannot detect performance degradations on a website of less than 200ms. Browser's JavaScript adds less than 15ms in aggregated time per page load. This is split up over time, so at no point would a user be able to perceive any performance impact due to the JavaScript.
- Webserver and systems: Browser app monitoring occurs on the user's browser, not on the server. Processing time does not have an impact on your CPU consumption.
In addition, we take additional steps to minimize any potential impact on the apps and webpages being monitored. For example, the "loader" script is loaded synchronously in the <HEAD> in order to ensure monitoring is enabled for the entire life cycle of the page. This script is included inline, which eliminates the need for another roundtrip network request to a content delivery network (CDN). The "loader" comes with the initial page load.
Later in the life cycle of the page, New Relic loads an additional monitoring script asynchronously. This script should not have any perceivable effect to the user and is included in the overall overhead of less than 15ms per page.
Network impact
Browser monitoring also minimizes network traffic for the end user by aggregating data locally (in the client) and sending it back to New Relic on load, at periodic intervals, on unload, or when data has been collected. (During the browser session's idle periods, transmissions may not be required.)
For more help
Additional documentation resources include:
- Instrumentation for page load timing (JavaScript elements, data transmission)
- Browser monitoring and search engine optimization (how browser ensures that the JavaScript has a negligible impact on SEO)