Yoav Reisler


Introduction Seven Essential JavaScript Functions for Developers

As a developer, you might know how important JavaScript has become. Right now, it is the most popular and commonly used programming language in the world. It is used to program desktop and server programs, webpages, web applications, mobile applications, etc. It is also used for databases like MongoDB and CouchDB.

JavaScript has come a long way since its inception. Earlier, developers were aware of only a few functions for all types of features and functionalities because every browser implemented the features according to their rendering engines, which made manual testing of web applications across browsers complicated. But, now you can automate the cross-browser testing of JavaScript web applications with the help of online Selenium Grid without writing repetitive code.

Also, JavaScript now utilizes multiple functions that help developers do more than just simple tasks. These functions also include reusable code that enables developers to build something without writing repetitive code over and over again.

Essential JavaScript Functions

As mentioned above, there are multiple JavaScript functions like decodeURI, alert(), Validate(), onload(), etc. Here, we will be covering seven functions that each developer has in their collection for functional and performance ease.

1. Debounce

Debounce is a ground-breaking function for improving event-fueled performance. It works as a callback function that can be used multiple times for a given time frame. It is more useful when you need to assign a callback function to frequently-firing events.

Also, it can speed up events quickly. Most commonly, it is used with resize, scroll, and key events, and if you’re not using debounce with these events, then you’re doing it wrong. Below is an example of using a debounce function.

// Returns a function, that, as long as it continues to be invoked, will not
// be triggered. The function will be called after it stops being called for
// N milliseconds. If `immediate` is passed, trigger the function on the
// leading edge, instead of the trailing.
function debounce(func, wait, immediate) {
    var timeout;
    return function() {
        var context = this,
            args = arguments;
        var later = function() {
            timeout = null;
            if (!immediate) func.apply(context, args);
        var callNow = immediate && !timeout;
        timeout = setTimeout(later, wait);
        if (callNow) func.apply(context, args);
// Usage
var myEfficientFn = debounce(function() {
    // All the taxing stuff you do
}, 250);
window.addEventListener('resize', myEfficientFn);

2. getAbsoluteUrl

The name itself defines this function. getAbsoluteUrl is preferably used to get an absolute URL from a variable string. Normally, it’s very difficult to get an absolute URL from variable strings, but using this function, it can be done quickly. getAbsoluteUrl can act as an alternative to the URL constructor, but it can be tricky to use if you don’t provide the required arguments regularly. Here’s an example to get an absolute URL with this function:

var getAbsoluteUrl = (function() {
    var a;
    return function(url) {
        if (!a) a = document.createElement('a');
        a.href = url;
        return a.href;
// Usage
getAbsoluteUrl('/something'); // https://davidwalsh.name/something

3. insertRule

This JavaScript function allows you to insert a CSS rule into your current stylesheet. insertRule is more useful because it enables you to change the stylesheet halfway down the line, which means you don’t have to go back and customize the entire stylesheet.

In JavaScript applications, this function is also used to grab a NodeList from a selector to give it a particular style and then set it to the selector. Therefore, you’ll not have to style each element to match the selector. You can set a style to selector like this:

var sheet = (function() {
    // Create the <style> tag
    var style = document.createElement('style');
    // Add a media (and/or media query) here if you'd like!
    // style.setAttribute('media', 'screen')
    // style.setAttribute('media', 'only screen and (max-width : 1024px)')
    // WebKit hack :(
    // Add the <style> element to the page
    return style.sheet;
// Usage
sheet.insertRule("header { float: left; opacity: 0.8; }", 1);

4. isNative

isNative gives you the freedom to tell whether a function is native or not. Though it seems irrelevant to JavaScript applications, it is actually very important. Knowing whether a function is native or not will help you know the risk of superseding it.

And, when you already know the risks, it will keep things in perspective. Also, if you make a mistake while overriding it, inNative can help you figure out why this happened. The following code will explain it better to you.

(function() {
    // Used to resolve the internal `[[Class]]` of values
    var toString = Object.prototype.toString;
    // Used to resolve the decompiled source of functions
    var fnToString = Function.prototype.toString;
    // Used to detect host constructors (Safari > 4; really typed array specific)
    var reHostCtor = /^\[object .+?Constructor\]$/;
    // Compile a regexp using a common native method as a template.
    // We chose `Object#toString` because there's a good chance it is not being mucked with.
    var reNative = RegExp('^' +
        // Coerce `Object#toString` to a string
        // Escape any special regexp characters
        .replace(/[.*+?^${}()|[\]\/\\]/g, '\\$CODE')
        // Replace mentions of `toString` with `.*?` to keep the template generic.
        // Replace thing like `for ...` to support environments like Rhino which add extra info
        // such as method arity.
        .replace(/toString|(function).*?(?=\\\()| for .+?(?=\\\])/g, '$1.*?') + '
    function isNative(value) {
        var type = typeof value;
        return type == 'function'
        // Use `Function#toString` to bypass the value's own `toString` method
        // and avoid being faked out.
        ? reNative.test(fnToString.call(value))
        // Fallback to a host object check because some environments will represent
        // things like typed arrays as DOM methods which may not conform to the
        // normal native pattern.
        : (value && type == 'object' && reHostCtor.test(toString.call(value))) || false;
    // export however you want
    module.exports = isNative;
// Usage
isNative(alert); // true
isNative(myCustomFunction); // false

5. once

Sometimes, developers prefer a given functionality happen only once; this function enables you to do that. The once function is almost like the onload event; it only runs one time for a page, thus avoiding duplicate initializations.

Also, this function is not called in a certain way because it is used while calling a function, not when defining a function. You can use once with any existing functions, even within external libraries.

function once(fn, context) {
    var result;
    return function() {
        if (fn) {
            result = fn.apply(context || this, arguments);
            fn = null;
        return result;
// Usage
var canOnlyFireOnce = once(function() {
canOnlyFireOnce(); // "Fired!"
canOnlyFireOnce(); // nada

6. poll

The poll function is amongst those functions that make things easier. What makes this function more useful is that it allows developers to periodically “pol” the server and request new information like new emails, messages, etc. After the server receives the request, it sends the information to the client. It happens automatically again and again for a certain period of time, thus giving the users the freedom from checking updates manually. Below is an example of using a polling function:

// The polling function
function poll(fn, timeout, interval) {
    var endTime = Number(new Date()) + (timeout || 2000);
    interval = interval || 100;
    var checkCondition = function(resolve, reject) {
        // If the condition is met, we're done!
        var result = fn();
        if (result) {
        // If the condition isn't met but the timeout hasn't elapsed, go again
        else if (Number(new Date()) < endTime) {
            setTimeout(checkCondition, interval, resolve, reject);
        // Didn't match and too much time, reject!
        else {
            reject(new Error('timed out for ' + fn + ': ' + arguments));
    return new Promise(checkCondition);
// Usage: ensure element is visible
poll(function() {
    return document.getElementById('lightbox').offsetWidth > 0;
}, 2000, 150).then(function() {
    // Polling done, now do something else!
}).catch(function() {
    // Polling timed out, handle the error!

7. matchesSelector

The matchesSelector function helps developers to verify whether an element of a given selector matches or not. This allows you to validate an element before moving ahead. This function can reduce the number of errors that most developers get down the line.

However, if you’re unable to validate the element, then you can make changes here and there, rather than identifying from where the error is coming. In short, using the matchesSelector function ensures that an element qualifies for moving forward. Here’s an example to show how matchesSelector works:

function matchesSelector(el, selector) {
    var p = Element.prototype;
    var f = p.matches || p.webkitMatchesSelector || p.mozMatchesSelector || p.msMatchesSelector || function(s) {
        return [].indexOf.call(document.querySelectorAll(s), this) !== -1;
    return f.call(el, selector);
// Usage
matchesSelector(document.getElementById('myDiv'), 'div.someSelector[some-attribute=true]')


The popularity behind JavaScript is its functionality that makes web applications more dynamic, and these functions can help you enhance your knowledge of JavaScript, as well as improve your programs. Many developers are well-versed with JavaScript, and they should be because most of the programs are either built on JavaScript or use some component that is built on JavaScript. Having knowledge of these functions will help you showcase your skills in JavaScript and will help you make things easier.

#js #javascript

What is GEEK

Buddha Community

Introduction Seven Essential JavaScript Functions for Developers

Hire Dedicated JavaScript Developers -Hire JavaScript Developers

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Ajay Kapoor


JS Development Company India | JavaScript Development Services

PixelCrayons: Our JavaScript web development service offers you a feature-packed & dynamic web application that effectively caters to your business challenges and provide you the best RoI. Our JavaScript web development company works on all major frameworks & libraries like Angular, React, Nodejs, Vue.js, to name a few.

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Ajay Kapoor


JS Development Company India | JavaScript Development Services

PixelCrayons’ JavaScript web development service offers you a feature-packed & dynamic web application that effectively caters to your business challenges and provide you the best RoI. Our JavaScript web development company works on all major frameworks & libraries like Angular, React, Nodejs, Vue.js, to name a few.

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Javascript Web Development Company

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Fredy  Larson

Fredy Larson


How long does it take to develop/build an app?

With more of us using smartphones, the popularity of mobile applications has exploded. In the digital era, the number of people looking for products and services online is growing rapidly. Smartphone owners look for mobile applications that give them quick access to companies’ products and services. As a result, mobile apps provide customers with a lot of benefits in just one device.

Likewise, companies use mobile apps to increase customer loyalty and improve their services. Mobile Developers are in high demand as companies use apps not only to create brand awareness but also to gather information. For that reason, mobile apps are used as tools to collect valuable data from customers to help companies improve their offer.

There are many types of mobile applications, each with its own advantages. For example, native apps perform better, while web apps don’t need to be customized for the platform or operating system (OS). Likewise, hybrid apps provide users with comfortable user experience. However, you may be wondering how long it takes to develop an app.

To give you an idea of how long the app development process takes, here’s a short guide.

App Idea & Research


_Average time spent: two to five weeks _

This is the initial stage and a crucial step in setting the project in the right direction. In this stage, you brainstorm ideas and select the best one. Apart from that, you’ll need to do some research to see if your idea is viable. Remember that coming up with an idea is easy; the hard part is to make it a reality.

All your ideas may seem viable, but you still have to run some tests to keep it as real as possible. For that reason, when Web Developers are building a web app, they analyze the available ideas to see which one is the best match for the targeted audience.

Targeting the right audience is crucial when you are developing an app. It saves time when shaping the app in the right direction as you have a clear set of objectives. Likewise, analyzing how the app affects the market is essential. During the research process, App Developers must gather information about potential competitors and threats. This helps the app owners develop strategies to tackle difficulties that come up after the launch.

The research process can take several weeks, but it determines how successful your app can be. For that reason, you must take your time to know all the weaknesses and strengths of the competitors, possible app strategies, and targeted audience.

The outcomes of this stage are app prototypes and the minimum feasible product.

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Vincent Lab

Vincent Lab


The Difference Between Regular Functions and Arrow Functions in JavaScript

Other then the syntactical differences. The main difference is the way the this keyword behaves? In an arrow function, the this keyword remains the same throughout the life-cycle of the function and is always bound to the value of this in the closest non-arrow parent function. Arrow functions can never be constructor functions so they can never be invoked with the new keyword. And they can never have duplicate named parameters like a regular function not using strict mode.

Here are a few code examples to show you some of the differences
this.name = "Bob";

const person = {
name: “Jon”,

<span style="color: #008000">// Regular function</span>
func1: <span style="color: #0000ff">function</span> () {
    console.log(<span style="color: #0000ff">this</span>);

<span style="color: #008000">// Arrow function</span>
func2: () =&gt; {
    console.log(<span style="color: #0000ff">this</span>);


person.func1(); // Call the Regular function
// Output: {name:“Jon”, func1:[Function: func1], func2:[Function: func2]}

person.func2(); // Call the Arrow function
// Output: {name:“Bob”}

The new keyword with an arrow function
const person = (name) => console.log("Your name is " + name);
const bob = new person("Bob");
// Uncaught TypeError: person is not a constructor

If you want to see a visual presentation on the differences, then you can see the video below:

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