Tutorial on using the debugger in Node.js

Posted in Tutorials

Let’s take the node.js application that we wrote in this tutorial and introduce a bug (typo) in the app.js file ….

When you run “node app.js” you get this error on the browser and console…

Using NodeJS Built in Debugger

You can use the built-in nodejs debugger by running …

node debug app.js

And you will get the nodejs debugger prompt at the console…

Here are the common commands that you can type in the debug prompt …

cont – continue

next – run next statement

step – step into the next statement

out – step out of the current function

backtrace – show callstack

repl – start node REPL (Read-Eval-Print Loop) for interactive javascript and viewing variables

watch(expression) – add expression to watch list

list(n) – list the n lines of code around current line.

setBreakpoint(n) – setbreakpoint at line n

Here we show example, where we run next line, set breakpoint at line 5 and “cont” to that breakpoint…

Next we start REPL, examine “app” and determined that it was a function, and view the value of “__dirname”…

Ctrl-C to exit REPL.

Ctrl-C twice to exit debugger.

 

 

 

 

---