A jQuery plugin for tracking HTML "coverage" of jQuery selectors - it helps you figure out which selectors aren't actually selecting any elements, which may signify dead code.

jQuery-coverage.js

/*
 Include using
 <script type="text/javascript" src="https://cdn.rawgit.com/drmercer/7da5b9dbe1a3e0b3ccc43c7fff8a1ec5/raw/86dba4b108a0ac3f1889f06c9db9454d88f770b1/jQuery-coverage.js"></script>
 
 Be sure to include it after you've loaded jQuery.
 */

window.jqcoverage = (function ($) {
	"use strict";

	function log(...args) {
		console.log("%c[jQuery-coverage]", "color:aqua", ...args);
	}
	
	// Configuration stuff (stores settings in localStorage)

	const KEY_SELECTORS = "jQuery-coverage-badSelectors";
	const badSelectors = JSON.parse(localStorage.getItem(KEY_SELECTORS)) || [];
	
	const KEY_BLACKLIST = "jQuery-coverage-blacklist";
	const blacklistedSelectors = JSON.parse(localStorage.getItem(KEY_BLACKLIST)) || [];
	function saveBlacklist() {
		localStorage.setItem(KEY_BLACKLIST, JSON.stringify(blacklistedSelectors));
	}

	const KEY_LOG_ENABLED = "jQuery-coverage-logEnabled";
	var logBadSelectors = JSON.parse(localStorage.getItem(KEY_LOG_ENABLED) || "true");
	function saveLogEnabledSetting() {
		localStorage.setItem(KEY_LOG_ENABLED, JSON.stringify(logBadSelectors));
	}

	if (badSelectors.length) {
		log("Loaded " + badSelectors.length + " bad selectors from a previous run");
		if (!logBadSelectors) {
			log("(Logging disabled. Call jqcoverage.enableBadSelectorLogging() to enable)");
		}
	}

	// This object is made global, so you can use it from the dev console. More functions below.
	const jqcoverage = {
		disableBadSelectorLogging: function () {
			logBadSelectors = false;
			saveLogEnabledSetting();
			log("Bad selector logging disabled");
		},
		enableBadSelectorLogging: function () {
			logBadSelectors = true;
			saveLogEnabledSetting();
			log("Bad selector logging enabled");
		},
	};


	// Create proxy jQuery function:
	const coverageMap = {};
	const new$ = function (...args) {
		const $res = $(...args);

		const key = args.join();

		const prevCount = coverageMap[key] || 0;
		const newCount = Math.max($res.length, prevCount);
		coverageMap[key] = newCount;

		// Warn when bad selectors are used again, to give the dev a stack trace
		if (logBadSelectors &&
				newCount === 0 &&
				badSelectors.includes(key) && 
				!blacklistedSelectors.includes(key)) {
			console.warn("Bad selector used: ", ...args);
		}

		return $res;
	};
	$.extend(new$, $);
	window.jQuery = new$;
	if (window.$ === $) {
		window.$ = new$;
	}
	
	//==============================================
	//       Coverage report tools

	// Call this to get a coverage report
	jqcoverage.getCoverage = function () {
		const summary = {};
		$.each(coverageMap, function (key, val) {
			summary[val] || (summary[val] = []);
			summary[val].push(key);
		});
		return summary;
	};
	
	jqcoverage.getCoverageOf = function(selector) {
		selector = "" + selector;
		var useCount = coverageMap[selector] || 0;
		return selector + " selected at most " + useCount + " element(s)";
	};

	// Call this to save the list of bad selectors to localStorage
	jqcoverage.saveBadSelectors = function () {
		const badSelectors = jqcoverage.getCoverage()[0] || [];
		localStorage.setItem(KEY_SELECTORS, JSON.stringify(badSelectors));
		const badSelectorCount = badSelectors.length;
		log("Saved " + badSelectorCount + " bad selectors to analyze on a later run");
	};

	// Call this to clear the list of bad selectors inlocalStorage and memory
	jqcoverage.clearBadSelectors = function () {
		localStorage.removeItem(KEY_SELECTORS);
		badSelectors.splice(0);
	};
	
	//==============================================
	//       Key blacklisting tools
	
	jqcoverage.blacklistSelector = function (selector) {
		if (typeof selector !== "string") {
			throw new Error("Selector must be a string");
		}
		if (!blacklistedSelectors.includes(selector)) {
			blacklistedSelectors.push(selector);
		}
		saveBlacklist();
	};
	
	jqcoverage.unblacklistSelector = function (selector) {
		var idx = blacklistedSelectors.indexOf(selector);
		if (idx !== -1) {
			blacklistedSelectors.splice(idx, 1);
			return "Selector removed from blacklist";
		} else {
			return "Selector not found in blacklist";
		}
		saveBlacklist();
	};

	log("jQuery-coverage loaded");
	return jqcoverage;

}(window.jQuery));