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Pages with Unused JS

Priority: Critical

Impact: Neutral

What issues it may cause​

When the JavaScript is render-blocking, the browser has to download, parse, compile, and evaluate the script before it can continue with the tasks necessary for rendering the page, which means users have to wait longer for the entire page to load because the browser is downloading and parsing unnecessary code.

Even when the JavaScript is asynchronous (non-render-blocking), it still uses bandwidth that could be used for other resources during the download process, which can impact performance. Transmitting unnecessary code over the network is also inefficient for mobile users with limited data plans.

Loading and parsing unused JavaScript can increase the time it takes for a page to become interactive, delaying the point at which users can start engaging with the page's content.

How do you fix it​

Identify and remove unused JavaScript.

Use Code Splitting to sivide JavaScript code into smaller chunks and only load the parts that are necessary for the current page or interaction.

Load JavaScript files asynchronously and only load code when it is needed, reducing the amount of unused code on the initial page load.

What is the positive impact​

  • Faster Page Load Times: Removing unused JavaScript reduces the amount of data that needs to be downloaded, speeding up page load times.

  • Reduced Network Usage: By minimizing unnecessary code, you can reduce network traffic and bandwidth usage.

  • Lower Memory Consumption: Removing unused code helps keep memory usage low, particularly important on devices with limited memory capacity.

How to fetch the data for this report template​

You will need to run a crawl for report template to generate report. When report has been generated and you have crawl id you can fetch data for the report using the following query:

query GetReportForCrawl($crawlId: ObjectID!, $reportTemplateCode: String!) {
  getCrawl(id: $crawlId) {
    reportsByCode(
      input: {
        reportTypeCodes: Basic
        reportTemplateCodes: [$reportTemplateCode]
      }
    ) {
      rows {
        nodes {
          ... on CrawlSiteSpeedAudits {
            url
            auditId
            title
            displayValue
            savingsKib
            pageviews
            productOfSavingsKibAndPageviews
            itemsCount
            auditResult
          }
        }
      }
    }
  }
}

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