What Are JavaScript Errors?
JavaScript errors are issues that prevent the code from executing as expected. These errors can be:
- Syntax Errors – Issues with the code structure.
- Runtime Errors – Issues that occur while the program runs.
- Logical Errors – Issues with the logic, producing incorrect results.
Types of JavaScript Errors
1) Syntax Error
Syntax errors occur when the code violates JavaScript’s syntax rules. These errors prevent the script from running.
Example:
console.log("Hello World) // Missing closing quote
// Uncaught SyntaxError: Unexpected string
Solution:
Always ensure your code adheres to JavaScript syntax rules by double-checking quotes, brackets, and operators.
2) Reference Error
A reference error happens when you try to access a variable or function that does not exist.
Example:
console.log(x); // x is not defined
// Uncaught ReferenceError: x is not defined
Solution:
Declare variables before using them:
let x = 10;
console.log(x); // 10
3) Type Error
A type error occurs when an operation is performed on a value of the wrong type.
Example:
const num = 10;
num.toUpperCase(); // num is not a string
// Uncaught TypeError: num.toUpperCase is not a function
Solution:
Use appropriate methods for the data type:
const str = "Hello";
console.log(str.toUpperCase()); // "HELLO"
4) Range Error
A range error happens when a value is not within the allowable range.
Example:
const numbers = new Array(-5); // Invalid array length
// Uncaught RangeError: Invalid array length
Solution:
Ensure values fall within valid ranges:
const numbers = new Array(5);
console.log(numbers.length); // 5
5) Eval Error
Eval errors are related to the misuse of the eval() function. While rare, these errors can occur if eval() is used incorrectly.
Example:
eval("2 + 2"); // Works fine
Solution: Avoid using eval() unless absolutely necessary, as it can lead to security vulnerabilities.
6) URI Error
URI errors occur when invalid characters are used in encodeURI() or decodeURI().
Example:
decodeURI('%'); // Invalid URI
// Uncaught URIError: URI malformed
Solution: Use valid URIs:
const uri = encodeURI('https://example.com?name=John Doe');
console.log(uri); // "https://example.com?name=John%20Doe"
Handling JavaScript Errors
JavaScript provides tools to handle errors gracefully without stopping program execution.
1) Using try…catch Block
The try block contains code that might throw an error, and the catch block handles the error.
Example:
try {
let result = 10 / 0;
console.log(result); // Infinity
} catch (error) {
console.error("An error occurred:", error.message);
}
2) Using finally
The finally block executes regardless of whether an error occurs.
Example:
try {
let data = JSON.parse("{invalid JSON}");
} catch (error) {
console.error("Parsing error:", error.message);
} finally {
console.log("Execution completed.");
}
3) Throwing Custom Errors
You can throw custom errors using the throw statement.
Example:
function divide(a, b) {
if (b === 0) {
throw new Error("Division by zero is not allowed.");
}
return a / b;
}
try {
console.log(divide(10, 0));
} catch (error) {
console.error(error.message);
}
Common Debugging Tips
- Use Developer Tools
Use the browser’s developer tools (e.g., Chrome DevTools) to debug errors effectively. - Add Console Logs
Use console.log() statements to identify where the error occurs. - Use Linting Tools
Tools like ESLint can help detect errors in your code before execution. - Read Error Messages
JavaScript error messages provide detailed information about the type and location of the error.
Best Practices for Avoiding Errors
- Use Strict Mode: Enable “use strict”; to catch common coding mistakes.
- Write Modular Code: Break your code into smaller functions or modules.
- Validate User Input: Always validate inputs to avoid unexpected errors.
- Handle Edge Cases: Test your code with different scenarios to ensure reliability.
- Keep Libraries Updated: Use the latest versions of JavaScript libraries to avoid compatibility issues.