In this article we'll define the Time to Interactive metric in Blue Triangle and the methodology for measuring it in both Real User and Synthetic Monitoring.
The Time to Interactive (TTI) metric measures how long it takes a page to become interactive. "Interactive" is defined as the point where:
• The page has displayed useful content, which is measured with First Contentful Paint.
• Event handlers are registered for most visible page elements.
• The page responds to user interactions within 50 milliseconds.
The Time to Interactive (TTI) is determined by two methodologies—the Long Task Timing API and the frames per second (FPS). We capture timings using both methods if they are available and report back the lower value from the two methods as the TTI. If neither method produces a Time to Interactive value, nothing (or zero) will be returned for the page measurement.
Method 1 – Long Task Timing
Method 2 – Frames Per Second (FPS)
The second method we use to determine page slowdowns, or a disruption to interactivity, is by checking the FPS of a page load. We capture the timestamp for each frame and determine the first 5 second quiet window after the First Contentful Paint. Similar to Method 1, the quiet window and the metric marking "useful content displayed" are configurable.