debugging node.js child_process fork example on IntelliJ IDEA

Question

debugging node.js child_process fork example on IntelliJ IDEA

I am trying to debug the child_process example from here using IntelliJ IDEA 12.1.3 and node 10.10. When I run nodejs app.js from a terminal everything works. The console output displays as expected. However, when I debug the same script using IDEA there are no messages in console output and the app just sits there. This is what is in the console window:

/usr/bin/nodejs --debug-brk=58954 app.js
debugger listening on port 58954
debugger listening on port 58954

When I run the script in IDEA without the debugger attached, the script works as expected.

Why does attaching the debugger break the script?

node.js
intellij-idea
child-process

Answer 1

You can force the children to use a free port for debugging. InteliJ will automatically pick up the port chosen by the child process.

Here's an example:

// Determine if in debug mode. 
// If so, pass in a debug-brk option manually, without specifying port.
var startOpts = {};
var isInDebugMode = typeof v8debug === 'object';
if(isInDebugMode) {
     startOpts = {execArgv: ['--debug-brk']};
}
child_process.fork('./some_module.js', startArgs, startOpts);

Answer 2

looks like a bug in node.js fork to me: both parent and child processes receive --debug-brk=58954 switch and attempt to start debugger and listen port 58954.