Depricate Notice:

This project works. But there's a much better project with a similar API.
It even does not need a binary addon (So, it's easy to use).
See pidusage: https://github.com/soyuka/pidusage

• Simple interface to lookup cpu and memory usage of any accessible process on the system.
• Works on OSX, Linux, SmartOS and Solaris
• Tested on Heroku, Nodejitsu and Modulus

var usage = require('usage');

var pid = process.pid // you can use any valid PID instead
usage.lookup(pid, function(err, result) {

});

{
	memory: 100065280, // in no of bytes
	memoryInfo: {
		rss: 15966208, // resident size memory in bytes
		vsize: 3127906304 // virtual memory size in bytes
	},
	cpu: 10.6 // in percentage
}

This is only applicable for Linux

By default CPU Percentage provided is an average from the starting time of the process. It does not correctly reflect the current CPU usage. (this is also a problem with linux ps utility)

But If you call usage.lookup() continuously for a given pid, you can turn on keepHistory flag and you'll get the CPU usage since last time you track the usage. This reflects the current CPU usage.

see following example to enable keepHistory flag

var pid = process.pid;
var options = { keepHistory: true }
usage.lookup(pid, options, function(err, result) {

});

you can clear history cache too

usage.clearHistory(pid); //clear history for the given pid
usage.clearHistory(); //clean history for all pids