express-middleware-server-timing

express-middleware-server-timing

Automagic expressjs middleware performance monitoring.

There are many server-timing libraries out there for expressjs, but I couldn't find any that provided any out-of-the-box value.

Installation

npm install --save express-middleware-server-timing

Usage

const app = express()

// any time before `app.listen(...)`
require('express-middleware-server-timing')(app, [options])

The following table describes the properties of the options object.

Property	Description	Type	Default
name	name of the server timing metric	String	'mw'
description	description of the server timing metric	String	undefined
disabled	set true if you want to disable	Boolean	false

A server-timing entry named <name> (with optional description of <description>) will be generated for every request that passes through express.

Manual instrumentation

serverTimingStart / serverTimingStop

To create a server-timing entry reporting the duration between two check points of the same response, try:

app.get(path, function (req, res, next) {
  res.serverTimingStart('foo', 'bar')

  // some time later, maybe in different middleware handler
  res.serverTimingStop('foo')

  // ...
})

A header like this will be written to the response:

Server-Timing: foo; dur=[time in ms]; desc="bar"

serverTimingSync

To create a server-timing entry reporting the duration it took to execute a syncronous method, try:

app.get(path, function (req, res, next) {
  const result = res.serverTimingSync(function() {
    // slow syncronous code here
  }, 'slowMethod1', 'sometimes this method is slow')

  // ...
})

A header like this will be written to the response:

Server-Timing: slowMethod1; dur=[time in ms]; desc="sometimes this method is slow"

Browser Collection

For browsers that suport server-timing (Chrome 65+, Opera 52+), the entries can be accessed like this:

['navigation', 'resource']
  .forEach(function(entryType) {
    performance.getEntriesByType(entryType).forEach(function({name: url, serverTiming}) {
      serverTiming.forEach(function({name, duration, description}) {
        console.info('expressjs middleware =',
          JSON.stringify({url, entryType, name, duration, description}, null, 2))
      })
    })
})

Conditionally disable (example: based on environment)

require('express-middleware-server-timing')(app, {
  disabled: process.env.NODE_ENV === 'production'
})

License

MIT