Faster, better AI-powered code reviews. Start your free trial! 
Are you a web developer or coder working with JavaScript? Have you recently encountered an “Uncaught ReferenceError”? If so, you’ve certainly come to the right place. In this article, we’ll be exploring the “Uncaught ReferenceError”, as well as looking at ways to troubleshoot and resolve such issues. We’ll also go over some best practices, tips, and tricks for avoiding these types of errors in future.
What is an Uncaught ReferenceError?
An “Uncaught ReferenceError” is a type of JavaScript error. It usually appears when the code is attempting to access an undeclared variable. In other words, when the script calls for a variable that hasn’t been declared yet, the “Uncaught ReferenceError” will be thrown.
Here’s an example: imagine you have a script that prints out the value of a variable called “num”. But if you don’t declare the “num” variable anywhere in the code, you’ll get an “Uncaught ReferenceError” saying that “num is not defined.”
It’s important to note that the “Uncaught ReferenceError” is not the same as a “ReferenceError”. The “Uncaught ReferenceError” is thrown when the code is attempting to access an undeclared variable, while a “ReferenceError” is thrown when the code is attempting to access a declared variable that has not been assigned a value.
Causes of the Uncaught ReferenceError
When it comes to decoding the cause of an “Uncaught ReferenceError”, the key is often to look at the context in which the error is being thrown. To do this, you need to look at your code comments, as this will often give you insight into how the code is interacting with variables.
For example, improper variable declaration using ‘let’, ‘const’, and ‘var’ can lead to unexpected scoping issues and ReferenceErrors:
function myFunction() {
let x = 10; // x is only available in myFunction
const y = 20; // y is only available in myFunction
var z = 30; // z is available throughout
}
To demonstrate scoping rules, consider this code:
function myFunction() {
const a = 40;
if(true) {
const b = 50; // b is only available in if block
}
console.log(b); // Uncaught ReferenceError since b is not defined here
}
If your comment outlines that you need to call a certain function before attempting to access a variable, and you failed to do this, your code will throw the Uncaught ReferenceError. On the other hand, if you declared the variable outside of a function before trying to use it, but forgot to define it inside the function, your code will throw the same Uncaught ReferenceError.
In addition, if you are using a library or framework, such as jQuery, and you are attempting to access a variable that is not defined in the library, you will also get an Uncaught ReferenceError. It is important to check the documentation of the library or framework to ensure that the variable you are trying to access is defined.
Proactively avoiding Uncaught ReferenceErrors through proper variable declaration results in more seamless web app functionality and user experience.
How to Troubleshoot the Error
Once you understand what type of “Uncaught ReferenceError” you’re dealing with, it’s time to get down to troubleshooting. If this is your first time dealing with this error, you might not know where to start. Fortunately, there are some strategies that could help you out.
For a start, double-check all of your comments, as they contain vital information that isn’t necessarily brought to life by code. Make sure that any variables are being declared before they are accessed. And check that they are also being set to the values that they need to be.
You should also be sure to check for spelling mistakes and typos in your code. Sometimes these simple errors can cause the “Uncaught ReferenceError” to be thrown. Additionally, you should check for formatting errors; for example javascript indentations.
It is also important to check for any missing or extra parentheses, brackets, and braces. These can cause the error to be thrown if they are not properly balanced. Additionally, you should check for any missing or extra semicolons, as these can also cause the error to be thrown.
Common Solutions to Resolve the Error
Now that we’ve gone over ways in which you can troubleshoot an “Uncaught ReferenceError”, it’s time to look at some solutions.
The first one of these is to make sure that each variable is declared and initialized properly. Always declare your variables and initiate them at the beginning of the script. You can use ‘const’ and ‘let’ keywords to declare block-scoped variables, and ‘var’ to declare function-scoped variables.
You should also try separating your code into logical sections. If you organized your code into sections, this can make debugging easier. You can also wrap certain parts of your code in try /catch blocks — the idea behind this being that the try part of these blocks can contain the code that could throw errors, and then the catch part will ‘catch’ any errors that are thrown.
For example:
// Declare variables at the top
let num1, num2;
// Function to add numbers
function addNumbers() {
// Use try/catch
try {
// Add numbers
const result = num1 + num2;
} catch (error) {
// Catch errors
console.log(error);
}
}
Another solution is to use a linter, which is a tool that can help you identify any potential errors in your code. A linter can help you find any syntax errors, as well as any potential issues with your code. This can be a great way to quickly identify any potential issues with your code.
Best Practices for Avoiding the Error
Now that we know what an “Uncaught ReferenceError” is and how to troubleshoot it, you might be wondering how you can avoid it in future. Thankfully there are some steps that you can take to minimize your risk:
- Always declare and initialize variables correctly.
- Follow the rules of scoping: understand when variables are global or local.
- Separate your code into logical sections.
- Double-check comments and make sure any variables needed are declared.
- Take advantage of debugging tools and IDEs that can highlight coding errors.
- Check for spelling mistakes and typos.
It’s also important to keep your code organized and well-structured. This will help you to identify any potential errors quickly and easily. Additionally, it’s a good idea to use a version control system such as Git to keep track of changes to your code. This will help you to identify any issues that may have been introduced in the past and make it easier to roll back to a previous version if necessary.
Tips for Debugging Javascript Code
When developing or dealing with complex Javascript code, debugging is essential. To help simplify this process, there are certain tips and tricks which you can apply.
- Using debugger statements: include ‘debugger’ (in lowercase) in scripts where you need a breakpoint. Once this statement is encountered, the code will pause at this point and allow you time to investigate.
- Making use of console functions: using log(), else and debug(), developers can display data within their web browser console – their Javascript console more specifically
- The use of Chrome DevTools: Chrome DevTools offer developers an array of different debugging tools and options so they can identify issues quickly and efficiently.
- Using breakpoints within Chrome DevTools: this allows developers to pause their code at certain points so they can investigate further
It is also important to remember that debugging is a process of trial and error. It is important to take your time and be methodical in your approach. Don’t be afraid to try different methods and techniques to identify the source of the issue.
Summary and Conclusion
In summary, an “Uncaught ReferenceError” is a type of Javascript error. It usually appears when the code is attempting to access an undeclared variable. To troubleshoot such errors, a developer should check their comments, double-check any variable declarations, and look for spelling mistakes and typos in their code. The code should also be separated into logical sections and wrapped in try/catch blocks where necessary. When it comes to avoiding these types of errors in future, best practices should be put into action– namely variable declarations should always be made at the start, along with understanding variable scoping rules. Finally, developers should also make use of various debugging techniques — such as debugger statements, Chrome DevTools and log() functions — in order to detect problems early and efficiently.
by the Bito team. 
