phantomas/modules/domQueries/domQueries.js

Headless Chromium-based web performance metrics collector and monitoring tool

/**
 * Analyzes DOM queries done via native DOM methods
 */
"use strict";

module.exports = (phantomas) => {
  phantomas.setMetric("DOMqueries"); // @desc number of all DOM queries @offenders
  phantomas.setMetric("DOMqueriesWithoutResults"); // @desc number of DOM queries that returned nothing @offenders
  phantomas.setMetric("DOMqueriesById"); // @desc number of document.getElementById calls @offenders
  phantomas.setMetric("DOMqueriesByClassName"); // @desc number of document.getElementsByClassName calls @offenders
  phantomas.setMetric("DOMqueriesByTagName"); // @desc number of document.getElementsByTagName calls @offenders
  phantomas.setMetric("DOMqueriesByQuerySelectorAll"); // @desc number of document.querySelector(All) calls @offenders
  phantomas.setMetric("DOMinserts"); // @desc number of DOM nodes inserts @offenders
  phantomas.setMetric("DOMqueriesDuplicated"); // @desc number of DOM queries called more than once
  phantomas.setMetric("DOMqueriesAvoidable"); // @desc number of repeated uses of a duplicated query

  //
  // TODO: pass events fired by page scoped code
  //

  // report DOM queries that return no results (issue #420)
  phantomas.on(
    "domQuery",
    function (type, query, fnName, context, hasNoResults) {
      // ignore DOM queries within DOM fragments (used internally by jQuery)
      if (context.indexOf("body") !== 0 && context.indexOf("#document") !== 0) {
        return;
      }

      if (hasNoResults === true) {
        phantomas.incrMetric("DOMqueriesWithoutResults");
        phantomas.addOffender("DOMqueriesWithoutResults", {
          query,
          node: context,
          function: fnName,
        });
      }
    }
  );

  // count DOM queries by either ID, tag name, class name and selector query
  // @see https://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#dom-document-doctype
  var Collection = require("../../lib/collection"),
    DOMqueries = new Collection();

  phantomas.on("domQuery", function (type, query, fnName, context) {
    phantomas.log(
      'DOM query: by %s - "%s" (using %s) in %s',
      type,
      query,
      fnName,
      context
    );
    phantomas.incrMetric("DOMqueries");

    // Don't count document fragments or not yet inserted elements inside duplicated queries
    if (
      context &&
      (context.indexOf("html") === 0 ||
        context.indexOf("body") === 0 ||
        context.indexOf("head") === 0 ||
        context.indexOf("#document") === 0)
    ) {
      DOMqueries.push(type + ' "' + query + '" (in ' + context + ")");
    }
  });

  phantomas.on("report", () => {
    DOMqueries.sort().forEach((query, count) => {
      if (count > 1) {
        phantomas.incrMetric("DOMqueriesDuplicated");
        phantomas.incrMetric("DOMqueriesAvoidable", count - 1);
        phantomas.addOffender("DOMqueriesDuplicated", { query, count });
      }
    });
  });
};