An Creation to the Efficiency API

by | Aug 10, 2022 | Etcetera | 0 comments

The Efficiency API measures the responsiveness of your live web tool on authentic shopper devices and neighborhood connections. It’s going to almost definitely lend a hand identify bottlenecks for your client-side and server-side code with:

  • shopper timing: Custom designed measurement of client-side JavaScript serve as potency
  • paint timing: Browser rendering metrics
  • helpful useful resource timing: Loading potency of property and Ajax calls
  • navigation timing: Internet web page loading metrics, along with redirects, DNS look-ups, DOM readiness, and additional

The API addresses plenty of problems similar to standard potency assessment:

  1. Developers often test systems on high-end PCs hooked as much as a handy guide a rough neighborhood. DevTools can emulate slower devices, then again it received’t always highlight real-world issues when nearly all of consumers are running a two year-old mobile hooked as much as airport WiFi.
  2. Third-party alternatives similar to Google Analytics are often blocked, leading to skewed results and assumptions. You may also bump into privacy implications in some countries.
  3. The Potency API can accurately gauge rather a large number of metrics upper than methods similar to Date().

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The following sections describe ways you’ll be capable of use the Potency API. Some wisdom of JavaScript and web page loading metrics is in reality helpful.

Potency API Availability

Most current browsers give a boost to the Potency API – along with IE10 and IE11 (even IE9 has limited give a boost to). You’ll stumble at the API’s presence the usage of:

if ('potency' in window) {
  // use Potency API

It’s not conceivable to fully Polyfill the API, so be wary about missing browsers. If 90% of your consumers are thankfully browsing with Internet Explorer 8, you’d most straightforward be measuring 10% of customers with further capable systems.

The API can be used in Internet Staff, which give a option to execute complex calculations in a background thread without halting browser operations.

Most API methods can be used in server-side Node.js with the standard perf_hooks module:

// Node.js potency
import { potency } from 'node:perf_hooks';
// or in No longer strange JS: const { potency } = require('node:perf_hooks');

console.log( );

Deno provides the standard Efficiency API:

// Deno potency
console.log( );

It is important to run scripts with the --allow-hrtime permission to permit high-resolution time measurement:

deno run --allow-hrtime index.js

Server-side potency is most often easier to guage and prepare because it’s relying on load, CPUs, RAM, onerous disks, and cloud provider limits. {{Hardware}} upgrades or process keep an eye on alternatives similar to PM2, clustering, and Kubernetes can be simpler than refactoring code.

The following sections pay attention to client-side potency as a result of this.

Custom designed Potency Size

The Potency API can be used to time the execution pace of your tool functions. You’ll have used or encountered timing functions the usage of Date():

const timeStart = new Date();
const timeTaken = new Date() - timeStart;

console.log(`runMyCode() accomplished in ${ timeTaken }ms`);

The Potency API supplies two primary benefits:

  1. Upper accuracy: Date() measures to the nearest millisecond, then again the Potency API can measure fractions of a millisecond (depending on the browser).
  2. Upper reliability: The patron or OS can business the device time so Date()-based metrics isn’t going to always be right kind. This means your functions could appear in particular gradual when clocks switch forward!

The Date() an equivalent is which returns a high-resolution timestamp which is ready at 0 when the process responsible for creating the file starts (the internet web page has loaded):

const timeStart =;
const timeTaken = - timeStart;

console.log(`runMyCode() accomplished in ${ timeTaken }ms`);

A non-standard efficiency.timeOrigin belongings can also return a timestamp from 1 January 1970 even supposing this isn’t available in IE and Deno.

See also  6 Ways to Spice up Ecommerce Gross sales [Without Discounting] becomes impractical when making more than a few measurements. The Potency API provides a buffer where you’ll be capable of report fit for later analysis thru passing a label determine to efficiency.mark():


init(); // run initialization functions


funcX(); // run some other function


An array of all mark units throughout the Potency buffer can be extracted the usage of:

const mark = potency.getEntriesByType('mark');

Example finish end result:


    detail: null
    duration: 0
    entryType: "mark"
    name: "start:app"
    startTime: 1000
    detail: null
    duration: 0
    entryType: "mark"
    name: "start:init"
    startTime: 1001
    detail: null
    duration: 0
    entryType: "mark"
    name: "end:init"
    startTime: 1100

The efficiency.measure() way calculates the time between two marks and also stores it throughout the Potency buffer. You move a brand spanking new measure determine, the start mark determine (or null to measure from the internet web page load), and the completing mark determine (or null to measure to the current time):

potency.measure('init', 'start:init', 'end:init');

A PerformanceMeasure object is appended to the buffer with the calculated time period. To procure this worth, you’ll be capable of each request an array of all measures:

const measure = potency.getEntriesByType('measure');

or request a measure thru its determine:


Example finish end result:

    detail: null
    duration: 99
    entryType: "measure"
    name: "init"
    startTime: 1001

The usage of the Potency Buffer

Along with marks and measures, the Potency buffer is used to robotically report navigation timing, helpful useful resource timing, and paint timing (which we’ll discuss later). You’ll obtain an array of all entries throughout the buffer:


By the use of default, most browsers provide a buffer that stores up to 150 helpful useful resource metrics. This will have to be enough for plenty of tests, then again you’ll be capable of building up or decrease the buffer prohibit if sought after:

// report 500 metrics

Marks can be cleared thru determine otherwise you’ll be capable of specify an empty worth to clear all marks:


In a similar fashion, measures can be cleared thru determine or an empty worth to clear all:


Monitoring Potency Buffer Updates

A PerformanceObserver can practice changes to the Potency buffer and run a function when explicit events occur. The syntax can be familiar while you’ve used MutationObserver to answer DOM updates or IntersectionObserver to come across when portions are scrolled into the viewport.

You will have to define an observer function with two parameters:

  1. an array of observer entries which have been detected, and
  2. the observer object. If necessary, its disconnect() way can be known as to prevent the observer.
function performanceCallback(file, observer) {

  file.getEntries().forEach(get entry to => {
    console.log(`determine    : ${ get entry to.determine }`);
    console.log(`kind    : ${ get entry to.kind }`);
    console.log(`start   : ${ get entry to.startTime }`);
    console.log(`period: ${ get entry to.period }`);


The function is passed to a brand spanking new PerformanceObserver object. Its practice() way is passed an array of Potency buffer entryTypes to have a look at:

let observer = new PerformanceObserver( performanceCallback );
observer.follow({ entryTypes: ['mark', 'measure'] });

In this example, together with a brand spanking new mark or measure runs the performanceCallback() function. While it most straightforward logs messages proper right here, it could be used to purpose a knowledge upload or make further calculations.

Measuring Paint Potency

The Paint Timing API is most straightforward available in client-side JavaScript and robotically information two metrics which may also be very important to Core Internet Vitals:

  1. first-paint: The browser has started to draw the internet web page.
  2. first-contentful-paint: The browser has painted the first necessary products of DOM content material subject material, similar to a heading or an image.
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The ones can be extracted from the Potency buffer to an array:

const paintTimes = potency.getEntriesByType('paint');

Be wary about running this forward of the internet web page has completely loaded; the values is probably not in a position. Each look ahead to the window.load fit or use a PerformanceObserver to observe paint entryTypes.

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Example finish end result:

    "name": "first-paint",
    "entryType": "paint",
    "startTime": 812,
    "duration": 0
    "name": "first-contentful-paint",
    "entryType": "paint",
    "startTime": 856,
    "duration": 0

A gradual first-paint is often ended in thru render-blocking CSS or JavaScript. The gap to the first-contentful-paint could be large if the browser has to procure a large image or render advanced parts.

Helpful useful resource Potency Size

Neighborhood timings for belongings corresponding to images, stylesheets, and JavaScript information are robotically recorded to the Potency buffer. While there is also little you’ll be capable of do to get to the bottom of neighborhood pace issues (moderately than decreasing file sizes), it’ll almost definitely lend a hand highlight issues of higher property, gradual Ajax responses, or badly-performing third-party scripts.

An array of PerformanceResourceTiming metrics can be extracted from the buffer the usage of:

const belongings = potency.getEntriesByType('helpful useful resource');

However, you’ll be capable of fetch metrics for an asset thru passing its entire URL:

const helpful useful resource = potency.getEntriesByName('');

Example finish end result:

    connectEnd: 195,
    connectStart: 195,
    decodedBodySize: 0,
    domainLookupEnd: 195,
    domainLookupStart: 195,
    duration: 2,
    encodedBodySize: 0,
    entryType: "resource",
    fetchStart: 195,
    initiatorType: "script",
    name: "",
    nextHopProtocol: "h3",
    redirectEnd: 0,
    redirectStart: 0,
    requestStart: 195,
    responseEnd: 197,
    responseStart: 197,
    secureConnectionStart: 195,
    serverTiming: [],
    startTime: 195,
    transferSize: 0,
    workerStart: 195

The following properties can be examined:

  • determine: Helpful useful resource URL
  • entryType: “helpful useful resource”
  • initiatorType: How the helpful useful resource was once initiated, similar to “script” or “link”
  • serverTiming: An array of PerformanceServerTiming units passed during the server throughout the HTTP Server-Timing header (your server-side tool would possibly send metrics to the consumer for added analysis)
  • startTime: Timestamp when the fetch started
  • nextHopProtocol: Neighborhood protocol used
  • workerStart: Timestamp forward of starting a Modern Web App Supplier Worker (0 if the request isn’t intercepted thru a Supplier Worker)
  • redirectStart: Timestamp when a redirect started
  • redirectEnd: Timestamp after without equal byte of without equal redirect response
  • fetchStart: Timestamp forward of the helpful useful resource fetch
  • domainLookupStart: Timestamp forward of a DNS appearance up
  • domainLookupEnd: Timestamp after the DNS appearance up
  • connectStart: Timestamp forward of putting in a server connection
  • connectEnd: Timestamp after putting in a server connection
  • secureConnectionStart: Timestamp forward of the SSL handshake
  • requestStart: Timestamp forward of the browser requests the helpful useful resource
  • responseStart: Timestamp when the browser receives the first byte of knowledge
  • responseEnd: Timestamp after receiving without equal byte or closing the connection
  • period: The adaptation between startTime and responseEnd
  • transferSize: The helpful useful resource size in bytes along with the header and compressed body
  • encodedBodySize: The helpful useful resource body in bytes forward of uncompressing
  • decodedBodySize: The helpful useful resource body in bytes after uncompressing

This example script retrieves all Ajax requests initiated during the Fetch API and returns the entire transfer size and period:

const fetchAll = potency.getEntriesByType('helpful useful resource')
  .filter( r => r.initiatorType === 'fetch')
  .scale back( (sum, provide) => {
    return {
      transferSize: sum.transferSize += provide.transferSize,
      period: sum.period += provide.period
  { transferSize: 0, period: 0 }

Navigation Potency Size

Neighborhood timings for unloading the previous internet web page and loading the existing internet web page are robotically recorded to the Potency buffer as a single PerformanceNavigationTiming object.

Extract it to an array the usage of:

const pageTime = potency.getEntriesByType('navigation');

…or thru passing the internet web page URL to .getEntriesByName():

const pageTiming = potency.getEntriesByName(window.location);

The metrics are identical to those for assets however as well as accommodates page-specific values:

  • entryType: E.g. “navigation”
  • kind: Each “navigate”, “reload”, “back_forward,” or “prerender”
  • redirectCount: The choice of redirects
  • unloadEventStart: Timestamp forward of the dump fit of the previous file
  • unloadEventEnd: Timestamp after the dump fit of the previous file
  • domInteractive: Timestamp when the browser has parsed the HTML and constructed the DOM
  • domContentLoadedEventStart: Timestamp forward of file’s DOMContentLoaded fit fires
  • domContentLoadedEventEnd: Timestamp after file’s DOMContentLoaded fit completes
  • domComplete: Timestamp after DOM construction and DOMContentLoaded events have completed
  • loadEventStart: Timestamp forward of the internet web page load fit has fired
  • loadEventEnd: Timestamp after the internet web page load fit and all property are available
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Usual issues include:

  • A chronic prolong between unloadEventEnd and domInteractive. This is able to indicate a gradual server response.
  • A chronic prolong between domContentLoadedEventStart and domComplete. This is able to indicate that internet web page start-up scripts are too gradual.
  • A chronic prolong between domComplete and loadEventEnd. This is able to indicate the internet web page has too many property or plenty of are taking too long to load.

Potency Recording and Analysis

The Potency API implies that you’ll collate real-world usage data and upload it to a server for added analysis. You would possibly use a third-party provider corresponding to Google Analytics to store the data, then again there’s an opportunity the third-party script could be blocked or introduce new potency problems. Your own solution can be customized for your prerequisites to verify monitoring does not impact other capacity.

Be wary of eventualities through which statistics can’t be determined — perhaps on account of consumers are on earlier browsers, blocking JavaScript, or in the back of an organization proxy. Understanding what data is missing can be further fruitful than making assumptions consistent with incomplete wisdom.

Ideally, your analysis scripts received’t negatively impact potency thru running complex calculations or uploading large quantities of knowledge. Consider the usage of web team of workers and minimizing the usage of synchronous localStorage calls. It’s always conceivable to batch process raw data later.

In any case, be wary of outliers similar to very rapid or very gradual devices and connections that adversely impact statistics. For example, if 9 consumers load a internet web page in two seconds then again the tenth critiques a 60 second download, the average latency comes out to nearly 8 seconds. A further cheap metric is the median decide (2 seconds) or the 90th percentile (9 in each and every 10 consumers experience a load time of 2 seconds or a lot much less).


Internet efficiency remains a essential issue for builders. Consumers expect internet sites and systems to be responsive on most devices. Search Engine Optimization can be affected as slower websites are downgraded in Google.
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There are lots of efficiency tracking gear out there, then again most assess server-side execution speeds or use a limited choice of capable consumers to judge browser rendering. The Potency API provides a option to collate authentic shopper metrics that it could not be conceivable to calculate each and every different manner.

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