next-rum

The next-rum component extracts RUM data when Next.js router based navigation is taking place in your application. This ensures that all previews and load times are correctly tracked when the /pages are used dynamically loaded by next instead of a full server refresh / reload.

Installation

npm install --save next-rum

Usage

The library is designed as React component. The reason for this is because we know that if we get rendered by the Next client that all the required globals that we need to hook into are available in the global scope.

The component will not produce any output, and will return the children during render so you can use it as either a wrapper around your application or as standalone component that you just include in the bottom of your application:

import React, { Fragment } from 'react';
import App from './application';
import RUM from 'next-rum';
 
/**
 * Implement your custom tracker/analytics here to receive the RUM data.
 *
 * @param {String} url The URL that we navigated to.
 * @param {Object} rum The measured navigation data.
 * @private
 */
function navigated(url, rum) {
  console.log('the page has navigated to', url, rum);
}
 
//
// Example where it wraps your application code.
//
export default function WrappingApplication(props) {
  return (
    <RUM navigated={ navigated }>
      <App { ...props } />
    </RUM>
  );
}
 
//
// Example where it's used a normal standalone component.
//
export function Standalone(props) {
  return (
    <Fragment>
      <App { ...props } />
      <RUM navigated={ navigated } />
    </Fragment>
  );
}

The <RUM> component accepts the following properties:

navigated

The component is written to be library agnostic as possible, so we expose a completion callback for when the page is navigated that will receive all relevant timing information. You can use this callback to transfer RUM information to the backend / service of your choosing.

This property is required

• path string, The path of the site that we've navigated to.
• rum object, The navigation timing that we've extracted.

/**
 * Example to send data to Google Analytics
 *
 * @param {String} path Path of the new page.
 * @param {Object} rum Navigation timing.
 * @private
 */
function navigated(path, rum) {
  for (let metricName in rum) {
    ga('send', 'event', {
      eventCategory: 'Performance Metrics',
      eventValue: rum[metricName],
      eventAction: metricName,
      nonInteraction: true,
    });
  }
}
 
export default function Example() => {
  return (
    <RUM navigated={ navigated }>
      <Application />
    </RUM>
  );
}

clearResourceTimings

This will clear all the resource timing information that the browser has stored right before we are about to navigate to a new page. This ensures that there's enough room in the resource buffer, as well as makes it easier to find the start and end resources that your page might have loaded.

This is on by default, but you can turn it off if needed, it not, no touchy.

<RUM navigated={ navigated } clearResourceTimings={ false } />

setResourceTimingBufferSize

Allows you to bump the resource limit of the performance browser API through the component. In most, if not all cases you do not need to bump this value as it default to ~150 resources, which is more than enough for most applications.

<RUM navigated={ navigated } setResourceTimingBufferSize={ 200 } />

delay

The next-rum component leverages the ResourceTiming API to more accurately generate the correct loading times of your component so it can include images and other assets that are loaded when the component is rendered. Unfortunately the ResourceTiming API only contains item that are fully loaded. As this component has no idea what you will be loading in the component, we will wait an x amount of milliseconds before we gather the data, and call the navigated callback. This gives assets some time to complete loading, so they can be included in the metrics.

This is on by default, with a value of 2000

<RUM navigated={ navigated } delay={ 5000 } />

Navigation Timing

The following timing information is gathered:

{
  navigationStart: <epoch>,   // `routeChangeStart`
  fetchStart: <epoch>,
  domainLookupStart: <epoch>,
  domainLookupEnd: <epoch>,
  connectStart: <epoch>,
  connectEnd: <epoch>,
  requestStart: <epoch>,
  responseStart: <epoch>,
  responseEnd: <epoch>,
  domLoading: <epoch>,        
  domInteractive: <epoch>,    // webVitals.loadEventStart
  domContentLoaded: <epoch>,
  domComplete: <epoch>,
  loadEventStart: <epoch>,    // webVitals.loadEventStart
  loadEventEnd: <epoch>
}

The navigationStart, loadEventStart, loadEventEnd, and renderDuration properties are gathered from Next.js built in web vitals metrics.

More details on the Next.js performance metrics can be found here, and more details on the gasket-next implimentation can be found here.

License

MIT