Prometheus exporter for Nodejs

Add a file named prometheus.js

var Register = require('prom-client').register; 
var Counter = require('prom-client').Counter;  
var Histogram = require('prom-client').Histogram; 
var Summary = require('prom-client').Summary;   
var ResponseTime = require('response-time'); 
 
/**
 \* A Prometheus counter that counts the invocations of the different HTTP verbs

 \* e.g. a GET and a POST call will be counted as 2 different calls
 `*/ 
 
module.exports.numOfRequests = numOfRequests = new Counter({
name: 'numOfRequests',
help: 'Number of requests made',
labelNames: ['method']
});

 
/**
 \* A Prometheus counter that counts the invocations with different paths

 \* e.g. /foo and /bar will be counted as 2 different paths
 */
 
module.exports.pathsTaken = pathsTaken = new Counter({
name: 'pathsTaken',
help: 'Paths taken in the app',
labelNames: ['path']
}); 
 
/**
 \* A Prometheus summary to record the HTTP method, path, response code and response time
 */

module.exports.responses = responses = new Summary({  
name: 'responses',
help: 'Response time in millis',
labelNames: ['method', 'path', 'status']
});
 
/** 
 \* This funtion will start the collection of metrics and should be called from within in the main js file 
 */ 
 
module.exports.startCollection = function () {  
  require('prom-client').collectDefaultMetrics();
}; 
 
/** 
 \* This function increments the counters that are executed on the request side of an invocation 

 \* Currently it increments the counters for numOfPaths and pathsTaken 
 */ 

module.exports.requestCounters = function (req, res, next) {  
  if (req.path != '/metrics') { 
​    numOfRequests.inc({ method: req.method }); 
​    pathsTaken.inc({ path: req.path }); 
  } 
  next(); 
} 
 
/** 
 \* This function increments the counters that are executed on the response side of an invocation 

 \* Currently it updates the responses summary 
 */ 

module.exports.responseCounters = ResponseTime(function (req, res, time) {  
  if(req.url != '/metrics') { 
​    responses.labels(req.method, req.url, res.statusCode).observe(time); 
  } 

}) 
 
/** 
 \* In order to have Prometheus get the data from this app a specific URL is registered 
 */ 

module.exports.injectMetricsRoute = function (App) {  
  App.get('/metrics', (req, res) => { 
​    res.set('Content-Type', Register.contentType); 
​    res.end(Register.metrics()); 
  }); 
}; 

Import Prometheus to application main file (app.js).

var Prometheus = require('./prometheus'); 

app.use(Prometheus.requestCounters); 

app.use(Prometheus.responseCounters); 

Prometheus.injectMetricsRoute(app); 

Prometheus.startCollection();