The Console object provides access to the browser's debugging console (e.g., the Web Console in Firefox). The specifics of how it works vary from browser to browser, but there is a de facto set of features that are typically provided.
Creates a new inline group in the Web Console. Unlike console.group(), however, the new group is created collapsed. The user will need to use the disclosure button next to it to expand it, revealing the entries created in the group.
Starts a timer you can use to track how long an operation takes. You give each timer a unique name, and may have up to 10,000 timers running on a given page. When you call console.timeEnd() with the same name, the browser will output the time, in milliseconds, that elapsed since the timer was started.