DevTools includes a full source level debugger, supporting breakpoints, stepping, and variable inspection.
When you open the debugger tab, you should see all the libraries for you application
listed in bottom left of the screen (under the
Scripts area), and the source for the
main entry-point for your app in the loaded in the main source area.
In order to browse around more of your application sources, you can scroll through
Scripts area and select other source files to display.
To set a breakpoint, click on the left margin (the line number ruler) in the source
area. Clicking once will set a breakpoint, which should also show up in the
Breakpoints area on the left. Clicking again will remove the breakpoint.
When your application encounters a breakpoint, it’ll pause there, and the DevTools
debugger will show the paused execution location in the source area. In addition,
Call stack and
Variables areas will 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 will change the contents of the
Variables area, you can inspect individual objects by toggling them open
to see their fields. Hovering over an object in the
Variables area will call the
toString() method for that object and display the result.
When paused, the three stepping buttons become active.
Step into step into a method invocation, stopping at the first executable line in that invoked method
Step overto step over a method invocation; this steps through source lines in the current method
Step outto step out of the current method, without stopping at any intermediary lines
In addition, the
Resume button will continue regular execution of the application.
Console output for the running app (stdout and stderr) is displayed in the console, below the source code area.
To adjust the break on exceptions behavior, toggle the
Break on unhandled exceptions
Break on all exceptions checkboxes in the upper right of the debugger UI.
Breaking on unhandled exceptions will only pause execution if the breakpoint is considered uncaught by the application code. Breaking on all exceptions will cause the debugger to pause whether or not the breakpoint was caught by application code.