How to find out the % CPU usage for Node.js process?

On *nix systems can get process stats by reading the /proc/[pid]/stat virtual file.

For example this will check the CPU usage every ten seconds, and print to the console if it's over 20%. It works by checking the number of cpu ticks used by the process and comparing the value to a second measurement made one second later. The difference is the number of ticks used by the process during that second. On POSIX systems, there are 10000 ticks per second (per processor), so dividing by 10000 gives us a percentage.

var fs = require('fs');

var getUsage = function(cb){
    fs.readFile("/proc/" + process.pid + "/stat", function(err, data){
        var elems = data.toString().split(' ');
        var utime = parseInt(elems[13]);
        var stime = parseInt(elems[14]);

        cb(utime + stime);
    });
}

setInterval(function(){
    getUsage(function(startTime){
        setTimeout(function(){
            getUsage(function(endTime){
                var delta = endTime - startTime;
                var percentage = 100 * (delta / 10000);

                if (percentage > 20){
                    console.log("CPU Usage Over 20%!");
                }
            });
        }, 1000);
    });
}, 10000);

Use node process.cpuUsage function (introduced in node v6.1.0). It shows time that cpu spent on your node process. Example taken from docs:

const previousUsage = process.cpuUsage();
// { user: 38579, system: 6986 }

// spin the CPU for 500 milliseconds
const startDate = Date.now();
while (Date.now() - startDate < 500);

// At this moment you can expect result 100%
// Time is *1000 because cpuUsage is in us (microseconds)
const usage = process.cpuUsage(previousUsage);
const result = 100 * (usage.user + usage.system) / ((Date.now() - startDate) * 1000) 
console.log(result);

// set 2 sec "non-busy" timeout
setTimeout(function() {
    console.log(process.cpuUsage(previousUsage);
    // { user: 514883, system: 11226 }    ~ 0,5 sec
    // here you can expect result about 20% (0.5s busy of 2.5s total runtime, relative to previousUsage that is first value taken about 2.5s ago)
}, 2000);

You can use the os module now.

var os = require('os');
var loads = os.loadavg();

This gives you the load average for the last 60seconds, 5minutes and 15minutes. This doesnt give you the cpu usage as a % though.

see node-usage for tracking process CPU and Memory Usage (not the system)

Another option is to use node-red-contrib-os package