An error in JavaScript is an object that represents a problem that occurs during program execution. When JavaScript encounters an error, it may stop executing the code unless the error is caught and handled using techniques like try...catch.
🔍 Common Types of JavaScript Errors
Here are the most common types of errors you’ll run into:
1. SyntaxError
Occurs when the JavaScript engine encounters code that breaks the syntax rules.
jsCopyEdit// Example:
let x = ; // SyntaxError: Unexpected token ';'
Fix: Make sure your code follows JavaScript syntax rules.
2. ReferenceError
Happens when a variable is used before it’s declared or not defined at all.
jsCopyEditconsole.log(myVar); // ReferenceError: myVar is not defined
Fix: Declare variables with let, const, or var before using them.
3. TypeError
Thrown when a value is not of the expected type or a method is called on a non-object.
jsCopyEditlet num = 5;
num.toUpperCase(); // TypeError: num.toUpperCase is not a function
Fix: Check data types and ensure you’re calling methods on appropriate values.
4. RangeError
Occurs when a value is not within an allowable range, such as when using numbers that are too large.
jsCopyEditlet arr = new Array(-5); // RangeError: Invalid array length
Fix: Make sure your values are within valid ranges.
5. EvalError (Rare)
Related to the misuse of the eval() function. It’s rare in modern JavaScript and often avoided.
jsCopyEditeval("alert('Hello');"); // Generally avoided due to security risks
6. URIError
Happens when global URI handling functions like decodeURI() are used incorrectly.
jsCopyEditdecodeURI('%'); // URIError: URI malformed
Fix: Check if the URI string is properly encoded.
🛠️ Handling Errors with try…catch
To prevent your entire script from crashing, you can use try...catch blocks to handle errors gracefully.
jsCopyEdittry {
let result = x + 10;
} catch (error) {
console.error('An error occurred:', error.message);
}
The try block contains the code that might fail, and the catch block handles any resulting errors.
✅ Best Practices
- Always validate inputs before performing operations.
- Use
typeoforArray.isArray()to check types before calling methods. - Don’t ignore errors; log them or display user-friendly messages.
- Avoid
eval()unless absolutely necessary.
🧾 Conclusion
JavaScript errors are inevitable, but understanding their types helps you debug faster and write better code. Whether it’s a SyntaxError due to a missing bracket or a TypeError from calling a method on the wrong type, knowing what each error means is key to solving the problem quickly.
By using proper error handling and writing clean, predictable code, you can prevent many common JavaScript bugs and build more robust application