JavaScript Idle Detection - Sal Ferrarello

Recently, I needed to determine when a website visitor was idle for a certain amount of time. I thought this was an interesting problem and wanted to spend a little more time with JavaScript so I wrote some code for it. Since we are monitoring idle time and I’m a big fan of the quote

Idle hands are the Devil’s Playground.

I called it “Devil’s Playground”.

Here is a copy of the JavaScript code, which is also available on GitHub at github.com/salcode/devils-playground.

	/**
	* Devils Playground.
	* JavaScript Idle Detection
	* Version: 0.2.0
	* License: apache-2.0
	* Project URL: https://github.com/salcode/devils-playground
	* Author: Sal Ferrarello
	* Author URL: https://salferrarello.com
	*
	* Usage:
	*
	* var idle = new DevilsPlayground(
	* function() {
	* alert('You have been idle for 42 seconds!');
	* },
	* 42,
	* {
	* 'devMode': false, // console.log() counter.
	* }
	* );
	* idle.start();
	*/
	'use strict';

	/**
	* Constructor.
	*
	* @param function idleFunction The function to execute after the number of
	* idle seconds pass.
	* @param int maxNumSeconds (optional) The maximum number of idle seconds
	* before the function is executed. Defaults
	* to 120 seconds (2 minutes).
	* @param object options (optional)
	* - bool devMode If the current counter and calls to reset
	* should be displayed in the JavaScript
	* console. Defaultsthe version I grew up hearing was "Devil's Playground".
	*/
	function DevilsPlayground(idleFunction, maxNumSeconds = 120, options = {} ) {

	this.idleFunction = idleFunction;
	this.maxNumSeconds = maxNumSeconds;
	this.secondCounter = 1;
	this.devMode = options.devMode \|\| false;

	this.addListeners();
	}

	/**
	* Start timer.
	*
	* Reset counter and start counting.
	*/
	DevilsPlayground.prototype.start = function() {
	this.stop();
	this.reset();
	this.continue();
	};

	/**
	* Stop timer.
	*/
	DevilsPlayground.prototype.stop = function() {
	clearTimeout(this.timer);
	};

	/**
	* Reset the second counter.
	*/
	DevilsPlayground.prototype.reset = function() {

	if(this.devMode) { console.log('reset'); }

	this.secondCounter = 1;
	};

	/**
	* Continue timer.
	*
	* Set the next tick to occur after delay.
	*/
	DevilsPlayground.prototype.continue = function() {
	var self = this;
	this.timer = setTimeout(function() {
	self.tick();
	}, 1000);
	};

	/**
	* Record time that has passed.
	*/
	DevilsPlayground.prototype.tick = function() {

	if(this.devMode) { console.log(this.secondCounter); }

	if (this.isSecondCounterMax()) {
	this.idleFunction();
	return;
	}

	this.secondCounter++;
	this.continue();
	};

	/**
	* Have we reached the maximum number of seconds?
	*
	* @return bool We are at the maximum number of seconds.
	*/
	DevilsPlayground.prototype.isSecondCounterMax = function() {
	return this.secondCounter >= this.maxNumSeconds;
	};

	/**
	* Assign listeners to note behavior that is not idle.
	*/
	DevilsPlayground.prototype.addListeners = function() {

	var self = this,
	options = this.isPassiveSupported() ? { passive: true } : false;

	document.addEventListener("mousemove", self.reset, options);
	document.addEventListener("mousedown", self.reset, options);
	document.addEventListener("keypress", self.reset, options);
	document.addEventListener("DOMMouseScroll", self.reset, options);
	document.addEventListener("mousewheel", self.reset, options);
	document.addEventListener("touchmove", self.reset, options);
	document.addEventListener("MSPointerMove", self.reset, options);
	};

	/**
	* Is the options object supported for addEventListener in this browser?
	*
	* @see https://developer.mozilla.org/en-US/docs/Web/API/EventTarget/addEventListener#Safely_detecting_option_support
	* @return bool The options object is supported in this browser.
	*/
	DevilsPlayground.prototype.isPassiveSupported = function() {
	var passiveSupported = false;
	try {
	var options = Object.defineProperty({}, "passive", {
	get: function() {
	passiveSupported = true;
	}
	});
	window.addEventListener("test", options, options);
	window.removeEventListener("test", options, options);
	} catch(err) {
	passiveSupported = false;
	}
	return passiveSupported;
	}

view raw devils-playground.js hosted with ❤ by GitHub

Sal Ferrarello (@salcode)

Sal is a PHP developer with a focus on the WordPress platform. He is a conference speaker with a background including Piano Player, Radio DJ, Magician/Juggler, Beach Photographer, and High School Math Teacher. Sal can be found professionally at WebDevStudios, where he works as a senior backend engineer.

Sal Ferrarello (@salcode)

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