JavaScript Useful Functions

A couple of useful JavaScript functions such as unifying events, debouncing or detecting mobile browsers

Apr 12, 2020

#javascript #webdev #programming #tools

Photo by Sam Moqadam on Unsplash

I share one trick a day until the original scheduled date of the end of the COVID-19 quarantine in Switzerland, April 19th 2020. Seven days left until this first milestone. Hopefully better days are ahead.

We are using a couple of JavaScript functions across the multiple applications and Web Components of DeckDeckGo.

Maybe these can be useful for your projects too?

Unifying Mouse And Touch Events

If you are implementing functions which have to do with user interactions through mouse or touch devices, there is a good change that their outcome are the same.

For example, presenters can draw over their presentations using our remote control. For such purpose we use canvas and are attaching events such as:

const canvas = document.querySelector("canvas"); canvas.addEventListener("mousedown", this.startEvent); canvas.addEventListener("touchstart", this.startEvent);

As you can notice, both mouse and touch events are handled by the same functions, which is good, but unfortunately, can’t work out without a bit of logic if you would like to access to positions information as for example clientX or clientY .

Indeed, touch positioning are not available at the root of the object but rather in an array changedTouches .

function startEvent($event) { // MouseEvent console.log($event.clientX); // TouchEvent console.log($event.changedTouches[0].clientX); }

That’s why, we are using a function we have called unifyEvents to get the positioning regardless of the devices.

export function unifyEvent($event) { return $event.changedTouches ? $event.changedTouches[0] : $event; }

Which can be use as the following:

function startEvent($event) { // TouchEvent and MouseEvent unified console.log(unifyEvent($event).clientX); }


I covered the topic debouncing with JavaScript in a previous article but if you are looking to add such feature to your application without any dependencies, here’s a function to do so.

export function debounce(func, timeout?) { let timer; return (...args) => { const next = () => func(...args); if (timer) { clearTimeout(timer); } timer = setTimeout(next, timeout && timeout > 0 ? timeout : 300); }; }

User Agent

Earlier this year, Google has announced its decision to drop support for the User-Agent string in its Chrome browser (article / GitHub).

Therefor the following methods should be used wisely, knowing they will have to be replaced in the future.

That being said, here are a couple of handy functions which help detects information about the type of browser or device.


Detect Mobile Browsers is providing an open source list of mobile devices which can be use to test our navigator to detect if the user is browsing or using the application on a mobile device or not.

export function isMobile() { if (!window || !navigator) { return false; } const a = navigator.userAgent || navigator.vendor || (window as any).opera; // Regex Source -> return ( /(android|bb\d+|meego).+mobile|avantgo|bada\/|blackberry|blazer|compal|elaine|fennec|hiptop|iemobile|ip(hone|od|ad)|iris|kindle|lge |maemo|midp|mmp|mobile.+firefox|netfront|opera m(ob|in)i|palm( os)?|phone|p(ixi|re)\/|plucker|pocket|psp|series(4|6)0|symbian|treo|up\.(browser|link)|vodafone|wap|windows ce|xda|xiino/i.test( a ) || /1207|6310|6590|3gso|4thp|50[1-6]i|770s|802s|a wa|abac|ac(er|oo|s\-)|ai(ko|rn)|al(av|ca|co)|amoi|an(ex|ny|yw)|aptu|ar(ch|go)|as(te|us)|attw|au(di|\-m|r |s )|avan|be(ck|ll|nq)|bi(lb|rd)|bl(ac|az)|br(e|v)w|bumb|bw\-(n|u)|c55\/|capi|ccwa|cdm\-|cell|chtm|cldc|cmd\-|co(mp|nd)|craw|da(it|ll|ng)|dbte|dc\-s|devi|dica|dmob|do(c|p)o|ds(12|\-d)|el(49|ai)|em(l2|ul)|er(ic|k0)|esl8|ez([4-7]0|os|wa|ze)|fetc|fly(\-|_)|g1 u|g560|gene|gf\-5|g\-mo|go(\.w|od)|gr(ad|un)|haie|hcit|hd\-(m|p|t)|hei\-|hi(pt|ta)|hp( i|ip)|hs\-c|ht(c(\-| |_|a|g|p|s|t)|tp)|hu(aw|tc)|i\-(20|go|ma)|i230|iac( |\-|\/)|ibro|idea|ig01|ikom|im1k|inno|ipaq|iris|ja(t|v)a|jbro|jemu|jigs|kddi|keji|kgt( |\/)|klon|kpt |kwc\-|kyo(c|k)|le(no|xi)|lg( g|\/(k|l|u)|50|54|\-[a-w])|libw|lynx|m1\-w|m3ga|m50\/|ma(te|ui|xo)|mc(01|21|ca)|m\-cr|me(rc|ri)|mi(o8|oa|ts)|mmef|mo(01|02|bi|de|do|t(\-| |o|v)|zz)|mt(50|p1|v )|mwbp|mywa|n10[0-2]|n20[2-3]|n30(0|2)|n50(0|2|5)|n7(0(0|1)|10)|ne((c|m)\-|on|tf|wf|wg|wt)|nok(6|i)|nzph|o2im|op(ti|wv)|oran|owg1|p800|pan(a|d|t)|pdxg|pg(13|\-([1-8]|c))|phil|pire|pl(ay|uc)|pn\-2|po(ck|rt|se)|prox|psio|pt\-g|qa\-a|qc(07|12|21|32|60|\-[2-7]|i\-)|qtek|r380|r600|raks|rim9|ro(ve|zo)|s55\/|sa(ge|ma|mm|ms|ny|va)|sc(01|h\-|oo|p\-)|sdk\/|se(c(\-|0|1)|47|mc|nd|ri)|sgh\-|shar|sie(\-|m)|sk\-0|sl(45|id)|sm(al|ar|b3|it|t5)|so(ft|ny)|sp(01|h\-|v\-|v )|sy(01|mb)|t2(18|50)|t6(00|10|18)|ta(gt|lk)|tcl\-|tdg\-|tel(i|m)|tim\-|t\-mo|to(pl|sh)|ts(70|m\-|m3|m5)|tx\-9|up(\.b|g1|si)|utst|v400|v750|veri|vi(rg|te)|vk(40|5[0-3]|\-v)|vm40|voda|vulc|vx(52|53|60|61|70|80|81|83|85|98)|w3c(\-| )|webc|whit|wi(g |nc|nw)|wmlb|wonu|x700|yas\-|your|zeto|zte\-/i.test( a.substr(0, 4) ) ); }


To detect if our user is using an Apple mobile devices, we can test the navigator against the keywords iPad|iPhone|iPod .

export function isIOS() { if (!window || !navigator) { return false; } const a = navigator.userAgent || navigator.vendor || (window as any).opera; return /iPad|iPhone|iPod/i.test(a); }


Likewise, we can reduce the query to iPad only to guess if the user is on an iPad.

export function isIPad() { if (!window || !navigator) { return false; } const a = navigator.userAgent || navigator.vendor || (window as any).opera; return /iPad/i.test(a); }


Likewise, you can detect if the client is using a specific browser as for final example Firefox.

export function isFirefox() { if (!window || !navigator) { return false; } const a = navigator.userAgent || navigator.vendor || (window as any).opera; return /firefox/i.test(a); }

Full screen

Our presentations can be edited and browse in standalone or in full screen mode, that’s why we have to detect such state. For such purpose, we compare the window.innerHeight to the screen.height , if these are equals, the browser is in full screen mode.

export function isFullscreen() { if (!window || !screen) { return false; } return window.innerHeight == screen.height; }

Remove Attribute From HTML String

Let say your DOM contains an element which you would like to parse to a string with the help of JavaScript.

<div contentEditable="true" style="color: #ff0000"> Red </div>; const div = document.querySelector("div").outerHTML;

For some reason, you might not be able to touch or clone the DOM element but would be interested to remove an attribute from string value anyway.

Respectively, you would be interested in such result:

<div style="color: #ff0000">Red</div>

To clean up or remove an attribute from a string you can use the following handy RegExp:

const result = div .replace(/(<.*?)(contentEditable="" |contentEditable="true" |contentEditable="false" |contentEditable) (.*?>)/gi, '$1$3');

Basically, it searches all attribute possibilities and create a new string containing what’s before and after the selection.

My favorite tricks of all of these 😉.


DeckDeckGo is open source, you can find the above functions in our GitHub repo or their related npm packages.

Stay home, stay safe!