cpu.js

var os = require('os');

function loadAvgCpus(){

	var cpus = os.cpus();

	var total=0;
	var idle =0;

	for (var i = 0; i<cpus.length ; i++) {
	    Object.keys(cpus[i].times).forEach(function(type){
	      total += parseFloat(cpus[i].times[type]);
	    });
	    idle += parseFloat(cpus[i].times.idle);
	};

	return {idle: idle, total: total};

}

var firstCpusMeasure = loadAvgCpus();

var setIntervalCpus = setInterval(function(){

	var secondCpusMeasure = loadAvgCpus();

    var cpusIdleDiff = secondCpusMeasure.idle - firstCpusMeasure.idle;
    var cpusTotalDiff = secondCpusMeasure.total - firstCpusMeasure.total;

    var usedCpus = 100 - (cpusIdleDiff / cpusTotalDiff)*100;
    var freeCpus = (cpusIdleDiff / cpusTotalDiff)*100;

    firstCpusMeasure = loadAvgCpus();

	console.log('usedCpus', usedCpus, 'freeCpus', freeCpus);

}, 1000);