Time to Interactive and Total Blocking Time

After the browser paints the page's first content, the browser still needs to paint the remainder of the content. Before it can paint an additional pixel, though, the browser needs to continue doing the work discussed in the previous chapters. That includes executing additional JavaScript, calculating layout changes, and loading additional resource files. While the browser is doing this work, visitors have begun to see elements appear on the page and, seeing these elements, visitors will want to begin interacting with the page. If the browser is still busy rendering the page, it will be unable to respond quickly to a visitor's interactions. This can lead to significant and frustrating delays for visitors.