Node.js v0.5.6 Manual & Documentation


Table Of Contents


Debugger

V8 comes with an extensive debugger which is accessible out-of-process via a simple TCP protocol. Node has a built-in client for this debugger. To use this, start Node with the debug argument; a prompt will appear:

% node debug myscript.js

debug>

At this point myscript.js is not yet running. To start the script, enter the command run. If everything works okay, the output should look like this:

% node debug myscript.js

debug> run debugger listening on port 5858 connecting...ok

Node's debugger client doesn't support the full range of commands, but simple step and inspection is possible. By putting the statement debugger; into the source code of your script, you will enable a breakpoint.

For example, suppose myscript.js looked like this:

// myscript.js

x = 5; setTimeout(function () { debugger; console.log("world"); }, 1000); console.log("hello");

Then once the debugger is run, it will break on line 4.

% ./node debug myscript.js

debug> run debugger listening on port 5858 connecting...ok hello break in #<an Object>.onTimeout(), myscript.js:4 debugger; ^ debug> next break in #<an Object>.onTimeout(), myscript.js:5 console.log("world"); ^ debug> print x 5 debug> print 2+2 4 debug> next world break in #<an Object>._onTimeout() returning undefined, myscript.js:6 }, 1000); ^ debug> quit A debugging session is active. Quit anyway? (y or n) y %

The print command allows you to evaluate variables. The next command steps over to the next line. There are a few other commands available and more to come type help to see others.

Advanced Usage

The V8 debugger can be enabled and accessed either by starting Node with the --debug command-line flag or by signaling an existing Node process with SIGUSR1.