5 Common Causes of JavaScript Errors (and How to Avoid Them)

JavaScript (JS) is a ubiquitous, flexible, and one of the top 10 programming languages for 2020 – though it is also prone to bugs and errors that make most developers frown and fool.

JS is widely used to enhance client-side user interactivity of most web applications. Without JavaScript, things on the web may be lifeless and unstimulating. Nevertheless, the ebbs and streams of language sometimes cause developers to have a love-hate relationship with it.

JavaScript errors cause applications to give unexpected results and damage the user experience. A recent study by the University of British Columbia (UBC) sought to find out the root causes and impact of JavaScript errors and errors. The results of the study revealed some common patterns that reduce the performance of JS programs.

In this blog post, we illustrate some of the common causes of JavaScript errors highlighted in the study (plus others we encounter daily) and how to make your applications less prone to errors.


The Document Object Model (DOM) plays an important role in the interactivity of websites. The DOM interface makes it possible to manipulate the content, style and structure of a web page. Making regular HTML web pages interactive – or manipulating DOM – is precisely why JavaScript programming languages were released.

So even with the introduction of backend JavaScript technologies like Node.js, working with DOM is still a big part of what language does. Therefore, DOM is a significant opportunity to introduce bugs and errors in JavaScript applications.

It is not surprising that the JavaScript bug report study found that DOM-related issues are responsible for most of the errors, 68%.
For example. Some JavaScript programmers often make the mistake of referring to a DOM element before it loads, leading to code errors.
document.getElementById (“container”) .innerHTML = “Common JS Errors and Errors”;

If the code above runs in the Chrome browser, it throws an error that can be seen on the Developer Console:

The error is thrown because JavaScript code is usually executed in the order it appears on a document. As such, the browser does not pay attention to the referenced item while the code is running.

To solve such a problem you can use different approaches. The simplest method is to place before the beginning of the script tag. You can also use a JavaScript library such as jQuery to make sure that the DOM is loaded first before it can be accessed.

document.getElementById (“container”) .innerHTML = “Common JS Errors and Errors”;


Syntax errors occur when the JavaScript interpreter does not execute a syntactically incorrect code. If you create an application and the interpreter observes symbols that do not conform to the default syntax of JavaScript programming languages, it will throw an error. According to the JavaScript Abdominal Report Survey, such errors account for 12% of all language errors.

Grammatical errors, such as missing parentheses or unsurpassed parentheses, are the main causes of syntax errors in JavaScript.

When you e.g. Need to use conditional statements to address multiple conditions, you may miss giving parentheses as needed, leading to syntax errors.

Let us look at the following example.

if ((x> y) && (y <77) { // more code here } Yes, the last parenthesis of the conditional statement is missing. Did you notice the error with the code above? Let's fix it. if ((x> y) && (y <77)) { // more code here }

To avoid such syntax errors, take the time to learn the grammatical rules of the JavaScript programming language. With comprehensive coding practices, you can easily find the grammatical errors and avoid sending them with your developed application.

Incorrect use of undefined / null keywords

Some JavaScript developers do not know how to use undefined and zero keywords correctly. In fact, the study reported that misuse of keywords accounts for 5% of all JavaScript errors. The zero keyword is an assignment value that is usually assigned to a variable to denote a non-existent value. surprisingly, zero is also a JavaScript object.

Here is an example:
var codeJS = null;
console.log (codeJS);
console.log (typeof codeJS);
// output is object
On the other hand, undefined indicates that a variable or any other property already declared lacks an assigned value. It may also indicate that nothing has been declared. undefined is a type of itself.
Here is an example:
was codeJS;
console.log (codeJS);
// output is not defined
console.log (typeof codeJS);
// output is not defined
It is interesting if the equality operator and the identity operator are used to comparing zero and undefined keywords, the latter do not consider them as equal.
console.log (null == undefined);
// output is true
console.log (null === undefined);
// output is incorrect
Therefore, knowing the correct use of zero and undefined keywords can help you avoid introducing bugs in your JavaScript programs.

Undefined methods

Another common cause of JavaScript errors is to call a method without giving its prior definition. UBC researchers found that this error results in 4% of all JavaScript errors.
Here is an example:
var codes = {
name: “Peter”,
age: 27,
speech () {
console.log (this.name);
coder.speakNow ();
Here is the bug seen on the Chrome Developer Console:

The above error occurs because the function called speakNow () is not defined in the JavaScript code.
Incorrect use of return statement

In JavaScript, the Return statement is used to stop the execution of a function so that its value can be read out. If used incorrectly, the return statement may impair the optimal performance of applications. According to the study, incorrect use of the return statement leads to 2% of all errors in JavaScript applications.

For example. Some JavaScript programmers usually make the mistake of breaking the return statement incorrectly.

While you can break a two-line JavaScript statement and still get the required output, the return statement breaks a disaster in your application.
Here is an example:
function number (s) {
was add = 5;
n + add;
console.log (number (10));

When the code above is run, an undefined error will appear on the Chrome Developer Console:
Therefore, you should refrain from breaking Return statements in your JavaScript code.


The client-side JavaScript programming language comes with excellent comprehensive capabilities to operate the functionalities of modern web applications. But if you do not understand the strange things that make the language work, the performance of your applications may be curled.

Moreover, JavaScript developers require versatile tools to troubleshoot the performance of their applications and to quickly detect bugs and errors.
Therefore, with a comprehensive suite of testing tools, you can reliably identify the anomalies that degrade the performance of your site. This is what you need to improve the performance of your website and achieve an optimal user experience.

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