Can we optimise this script to handle submission of metrics in SPAs

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Basit Qayoom

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Aug 12, 2024, 8:49:53 AM8/12/24

to web-vitals-feedback

import { onLCP, onINP, onCLS, onTTFB, onFCP, Metric } from "web-vitals";

/**
 * Represents a timestamp with milliseconds and date.
 *
 * @interface Timestamp
 */
interface Timestamp {
  /**
   * The timestamp in milliseconds.
   *
   * @type {number}
   */
  milliseconds: number;

  /**
   * The timestamp as a Date object.
   *
   * @type {Date}
   */
  date: Date;
}

/**
 * Represents the data returned from web vitals metrics.
 *
 * @interface ReturnedData
 */
interface ReturnedData {
  /**
   * An array of web vitals metrics.
   *
   * @type {Metric[]}
   */
  data: Metric[];

  /**
   * The timestamp when the data was collected.
   *
   * @type {?Timestamp}
   */
  timestamp?: Timestamp;

  /**
   * The location of the page where metrics were collected.
   *
   * @type {?Location}
   */
  location?: Location;
}

/**
 * The key used to store web vitals data in local storage.
 *
 * @type {string}
 */
const LOCAL_STORAGE_KEY = "pw-web-vitals";

/**
 * The expiration time for the stored data in milliseconds.
 *
 * @type {number}
 */
const EXPIRATION_TIME_MS = 1 * 60 * 1000; // 1 minute in milliseconds

// Initialize returnedData properly
/**
 * The data structure to store collected web vitals metrics.
 *
 * @type {ReturnedData}
 */
const returnedData: ReturnedData = {
  data: [], // Ensure data is initialized as an array
};

// Handle web vitals metrics
/**
 * Handles a web vitals metric by adding it to the returnedData if not already present.
 *
 * @param {Metric} metric - The web vitals metric to handle.
 */
const handleMetric = (metric: Metric) => {
  const { data } = returnedData;

  // Initialize location only once
  if (!returnedData.location) {
    returnedData.location = { ...window.location };
  }

  // Add new metric if it doesn't already exist and the array length is less than 5
  if (
    !data.some((existingMetric) => existingMetric.name === metric.name) &&
    data.length < 5
  ) {
    data.push(metric);
  }

  // Update the timestamp and store in local storage if 5 metrics are collected
  if (data.length === 5) {
    returnedData.timestamp = {
      milliseconds: Date.now(),
      date: new Date(),
    };

    saveWebVitalsData();
    // send to endpoint
  }

  // Log the updated returnedData
  console.log(returnedData);
};

// Save web vitals data to local storage
/**
 * Saves the web vitals data to local storage.
 */
const saveWebVitalsData = () => {
  const currentPath = returnedData.location!.pathname;
  const timestamp = returnedData.timestamp!.milliseconds;

  const storedDataString = localStorage.getItem(LOCAL_STORAGE_KEY);
  const webVitalsData: { [path: string]: number } = storedDataString
    ? JSON.parse(storedDataString)
    : {};

  // Update or add entry for the current path
  webVitalsData[currentPath] = timestamp;

  localStorage.setItem(LOCAL_STORAGE_KEY, JSON.stringify(webVitalsData));
};

// Main function to start monitoring metrics
/**
 * Starts monitoring web vitals metrics.
 */
function main() {
  onCLS(handleMetric);
  onFCP(handleMetric);
  onLCP(handleMetric);
  onTTFB(handleMetric);
  onINP(handleMetric);
}

// Initialize monitoring based on local storage data
/**
 * Initializes monitoring based on the data stored in local storage.
 */
function initializeMonitoring() {
  if (typeof window !== "undefined") {
    const webVitalsDataString = localStorage.getItem(LOCAL_STORAGE_KEY);

    try {
      if (!webVitalsDataString) {
        main();
        return;
      }

      const webVitalsData: { [path: string]: number } =
        JSON.parse(webVitalsDataString);
      const currentPath = window.location.pathname;
      const timestamp = webVitalsData[currentPath];

      if (timestamp) {
        // Check if data is expired
        if (Date.now() - timestamp > EXPIRATION_TIME_MS) {
          // Remove the expired data
          delete webVitalsData[currentPath];
          localStorage.setItem(
            LOCAL_STORAGE_KEY,
            JSON.stringify(webVitalsData)
          );

          // Start monitoring metrics
          main();
        }
      } else {
        // No data for current path, start monitoring metrics
        main();
      }
    } catch (error) {
      console.error("Error handling web vitals data:", error);
      main();
    }
  }
}

export { initializeMonitoring };

Barry Pollard

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Aug 12, 2024, 9:01:18 AM8/12/24

to Basit Qayoom, web-vitals-feedback

The Web Vitals currently cannot be measured for soft navigation as used by SPAs.

Chrome is currently experimenting with ways of enabling this, which are detailed in this post:
https://developer.chrome.com/docs/web-platform/soft-navigations-experiment

This can be enabled with the chrome://flags/#enable-experimental-web-platform-features flag.

Thanks,

Barry

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