Node Debugger

launch with

node debug app.js

Example app.js

function floop (i) {
  if (i > 0) {
    var decrementer = 10;
    while( decrementer-- > 0 ){
      i--;
    }
    floop(i);
  }
  return i;
}

floop(50);

Debug app.js

node debug app.js 

< Debugger listening on port 5858
connecting to port 5858... ok
break in app.js:12
 10 }
 11 
>12 floop(50);
 13 });
debug> 

Stepping

• cont - Continue execution
  alias c
• next - Step next
  alias n
• step - Step in
  alias s
• out - Step out
  alias o
• pause - Pause running code

Debugger Commands

Step Into the function

debug> s
break in app.js:2
  1 function floop (i) {
> 2   if (i > 0) {
  3     var decrementer = 10;
  4     while( decrementer-- > 0 ){

press s to step into the function

Watchers

debug> watch("decrementer");

watch("expr")
unwatch("expr")​

Watchers

debug> s
break in app.js:3
Watchers:
  0: decrementer = undefined

  1 function floop (i) {
  2   if (i > 0) {
> 3     var decrementer = 10;
  4     while( decrementer-- > 0 ){
  5       i--;

Step in
and the expression "decrementer" will be watched

Watchers

debug> s
break in app.js:4
Watchers:
  0: decrementer = 10

  2   if (i > 0) {
  3     var decrementer = 10;
> 4     while( decrementer-- > 0 ){
  5       i--;
  6     }

Keep stepping through and notice the watched epression

Watchers

debug> s
break in app.js:5
Watchers:
  0: decrementer = 9

  3     var decrementer = 10;
  4     while( decrementer-- > 0 ){
> 5       i--;
  6     }
  7     floop(i);

Keep stepping through and notice the watched epression

Unwatch Expression

unwatch("decrementer")

Setting Breakpoints

Set breakpoint on current line
setBreakpoint()

Set breakpoint on specific line
setBreakpoint(line #)

Set breakpoint on the first statement in function
setBreakpoint('fn()')

Set breakpoint on line n of script.js
setBreakpoint('script.js', 22)

alias : sb(args)

Set Breakpoint

debug> sb(7);

  1 function floop (i) {
  2   if (i > 0) {
  3     var decrementer = 10;
  4     while( decrementer-- > 0 ){
> 5       i--;
  6     }
* 7     floop(i);
  8   }
  9   return i;
 10 }

Continue

debug> c
break in app.js:7
  5       i--;
  6     }
> 7     floop(i);
  8   }
  9   return i;

c to continue

Clear Breakpoint

clearBreakpoint('app.js',7)
alias : cb(args)

Adding breakpoint 

with debugger;

debug> c
break in app.js:7
  5       i--;
  6     }
> 7     debugger;
  8     floop(i);
  9   }

debugger hanging?

keep pressing c and debugger will hang

kill with

killall node

manually exit from the process

add this to end of your script

process.exit();

Run and restart

press c until the process exits

debug> c
program terminated

run to start the terminated process

debug> run
< Debugger listening on port 5858
connecting to port 5858... ok

restart will restart the process

debug> restart
program terminated
< Debugger listening on port 5858
connecting to port 5858... ok

Node Inspector

install node-inspector with npm

npm i -g node-inspector

Start Node Inspector

install node-inspector with npm

node-debug app.js 
Node Inspector is now available from http://127.0.0.1:8080/?...
Debugging `app.js`

Debugger listening on port 5858

a browser should launch with will open with

a debugging session connected to your app process