3 Common Causes of JavaScript Errors and How To Avoid Them

We need to talk about JavaScript errors

Most of the articles discussing common causes of JavaScript errors online are surprisingly outdated. 

When you look at the first page of Google’s search results for “common JavaScript errors”, you may notice that nearly every post lists the same error types and cites this study from the University of British Columbia.

While that study is informative and relevant, the issue is… it was published in 2011.

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Why does this matter?

Since 2011, JavaScript has changed a lot. 

Maintaining an accurate understanding of common issues with the language is important for developers of all skill levels. After all, JavaScript is notoriously prone to errors and looking through developer forums confirms that reputation as Stack Overflow returns 2,346 separate questions tagged as “JavaScript” and “Error-Handling”. 

Even one of the original developers of JavaScript (and the creator of JSON), Douglas Crockford, recently said in an interview that “the best thing we can do today to JavaScript is to retire it.” 

So let’s discuss the elephant in the room and try to figure out a more current and accurate picture of what issues may be most common when coding in JavaScript in 2022.

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What are the most common causes of JavaScript errors?

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Updated categorization of JavaScript bugs

While there are many reports of individual bugs and complaints, comprehensive high-level studies on the subject can be hard to find.

However, one paper published in 2020 titled “BUGSJS: a benchmark and taxonomy of JavaScript bugs” provides us with a useful overview. 

Let’s take a look at this study and distill the error types listed within it into a quick guide. 

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 Most common causes of JavaScript bugs 

The most common causes of bugs in JavaScript code can be split into three categories:

1. Incomplete feature implementation
2. Incorrect feature implementation
3. General programming errors

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Categories of common JavaScript errors

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Incomplete feature implementation

This category encompasses 45% of all JavaScript bugs detected by BUGSJS. 

“Incomplete feature implementation” errors happen when the developers discover that their code’s features are missing some functionality. The bugs then appear because of new exceptions of of poorly implemented changes to features.

Specific errors in this category include:

• Incomplete data processing
• Missing input validation
• Error handling
• Incomplete configuration processing
• Incomplete output message

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Incorrect feature implementation

Incorrect feature implementation bugs were most common, as they made up 48% of all bugs observed in the study.

As opposed to issues with incomplete feature implementation, this category describes the bugs that appear despite the developers knowing what features they want their application to have. 

In this case, the code does not function as intended and fails to meet the requirements developers were trying to implement.

Specific errors in this category include:

• Incorrect data processing
• Incorrect input validation
• Incorrect filepath
• Incorrect output
• Incorrect configuration processing
• Incorrect handling of regex expressions
• Performance

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General programming errors

These are the bugs caused by any generic issues with coding. 

While these errors were a lot less common that the categories mentioned above, making up only 6% of the dataset, they are still important. After all, developers can make mistakes, and JavaScript can be easier to make a mistake in than other coding languages.

Specific errors in this category include:

• Typos
• Return statement issues
• Variable statements
• Incorrect data processing
• Missing type conversions
• Loop statement issues

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How to fix common JavaScript Errors

Now that we have figured out what errors are most common in JavaScript applications, let’s talk about how you can fix them.

According to the BUGSJS paper, 88% of errors were fixed with just 4 strategies:

1. Change an if statement
2. Change the expression of your return statement
3. Declare variables
4. Initialize empty variables

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Change an if statement

Especially if your bug is being caused by an issue with the scope of your features, you may simply need to rewrite some of your if statements. 

Try to modify each statement causing your problem or add another precondition.

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Change the expression of your return statement

You can try to change the return statement from 

return node.type !== "A";

To:

return !(node.type === "A" && lastI.type === "R");

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 Declare variables

While you don’t have to declare variables in JavaScript, this practice can cause unintended bugs and issues with scope or name clashes between variables.

So to fix it, just declare all the variables you’ve used in your code.

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Initialize empty variables

Add if statements to handle exceptions for values that are either undefined or null.

You can simply use the or  statement to do this.

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Other fixes

Of course, not all errors can be fixed with the above strategies.

While listing every single possible JavaScript error is outside the scope of our guide, there are some other patterns that you may benefit from.

The BUGSJS study also lists some other common fixes for JavaScript bugs. Those, together with the ones we’ve outlined above, can be found in the table below:

Other than that, you may need to consider your errors on a case by case basis. 

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Conclusion

37.3% of respondents to the 2021 State of JavaScript Survey agreed that developing in JavaScript is “overly complex”.

But if you know what errors are most common, what their underlying causes are, and how most JavaScript errors can be fixed you can save a lot of time and trouble.

To recap, the most common types of JavaScript errors are:

1. Incomplete feature implementation
2. Incorrect feature implementation
3. General programming errors.

And to fix those bugs you may benefit from trying one of the following steps:

1. Change an if statement
2. Change the expression of your return statement
3. Declare variables
4. Initialize empty variables.

Additionally, as your application scales, you might also consider a more powerful solution. 

Additional error handling tools can provide you with the complete context around any JavaScript error so that you can track down and resolve its root cause.

Railtown AI’s error logging and debugging solution can help you leverage the full power of JavaScript with automated insights and alerts powered by AI.

If you’re ready to move beyond basic logging and benefit from a robust solution, you can try Railtown AI for free.

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