The call stack and variable areas

When your application encounters a breakpoint, it pauses there,
and the DevTools debugger shows the paused execution location
in the source area. In addition, the Call stack and Variables
areas populate with the current call stack for the paused isolate,
and the local variables for the selected frame. Selecting other
frames in the Call stack area changes the contents of the variables.

Within the Variables area, you can inspect individual objects by
toggling them open to see their fields. Hovering over an object
in the Variables area calls toString() for that object and
displays the result.

Stepping through source code

When paused, the three stepping buttons become active.

Use Step in to step into a method invocation, stopping at
the first executable line in that invoked method.

Use Step over to step over a method invocation;
this steps through source lines in the current method.