Runtime errors in JavaScript occur during the execution of code when the JavaScript engine encounters an issue that prevents the program from continuing. These errors appear only after the code is successfully parsed and executed. These errors can arise due to invalid operations, incorrect assumptions, or unforeseen conditions during execution. Runtime errors are inevitable but manageable. By understanding their causes and using proper handling techniques developers can ensure their JavaScript applications are more robust and resilient to unexpected failures.
Common Types of Runtime Errors in JavaScript
1. ReferenceError
- Cause: Occurs when trying to access a variable or object that hasn’t been declared.
- Fix: Ensure that all variables are declared before use.
Example:
console.log(userName); // ReferenceError: userName is not defined
Fix:
let userName = "webner";
console.log(userName); // Output: webner
2. TypeError
- Cause: This happens when operating on a value of the wrong type (e.g., accessing a null property or calling a non-function).
- Fix: Ensure the value is of the correct type before operating.
Example:
let obj = null;
console.log(obj.name); // TypeError: Cannot read null property
Fix:
let obj = { name: "webner" };
console.log(obj.name); // Output: webner
3. RangeError
- Cause: Occurs when a value is outside the allowable range (e.g., creating an array with a negative size).
- Fix: Check the range or constraints before assigning values.
Example:
let arr = new Array(-5); // RangeError: Invalid array length
Fix:
let arr = new Array(5); // Creates an array with 5 empty slots
console.log(arr);
4. SyntaxError
- Cause: This happens when the eval() function encounters incorrect syntax.
- Fix: Validate the input string before using eval(), or avoid using eval() altogether.
Example:
eval("console.log('Hello)"); // SyntaxError: Unexpected end of input
Fix:
eval("console.log('Hello')"); // Output: Hello
5. URIError
- Cause: Occurs when encodeURI() or decodeURI() is used with an invalid URI.
- Fix: Ensure that the URI passed is properly formatted.
Example:
decodeURIComponent('%'); // URIError: URI malformed
Fix:
decodeURIComponent('%20'); // Output: " " (space character)
6. InternalError
- Cause: Rare error that occurs due to issues within the JavaScript engine (e.g., excessive recursion or memory allocation).
- Fix: Optimize the code to avoid deep recursion or large memory usage
In the end, to avoid Runtime errors we should use developer tools in the browser to trace errors and wrap the code to try and catch blocks and avoid deep recursion by using loops where possible.
