MCQs on Error Handling and Debugging | JavaScript Intermediate

Mastering error handling and debugging is crucial for developers to build reliable applications. This chapter covers try-catch statements, error types, debugging with consoles, and browser debugging tools.

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Error Handling and Debugging

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Topic: Try-Catch Statements

1. What does the try block in a try...catch statement do?
   • A) Executes code and logs errors automatically
   • B) Defines a block of code to be tested for errors
   • C) Suppresses all errors in the code
   • D) Executes only if no errors occur
2. Which block handles the error in a try...catch statement?
   • A) Try
   • B) Catch
   • C) Finally
   • D) Error
3. What happens if an error occurs in the try block?
   • A) The error is ignored
   • B) The program stops executing
   • C) The catch block is executed
   • D) The finally block executes
4. Which of the following is a valid syntax for try...catch in JavaScript?
   • A) try { code } catch { error }
   • B) try { code } catch (error) { handleError }
   • C) try (code) catch { error }
   • D) try { code } error (catch)
5. What is the purpose of the finally block in try...catch?
   • A) To execute if no error occurs
   • B) To clean up resources regardless of errors
   • C) To suppress errors
   • D) To log errors only
6. Can a try...catch statement have only a try block?
   • A) Yes, it is mandatory
   • B) No, a catch or finally block is required
   • C) Yes, but only in strict mode
   • D) No, it requires an error object
7. In a try...catch statement, what type of errors does the catch block handle?
   • A) Logical errors
   • B) Syntax errors
   • C) Runtime errors
   • D) All errors
8. What will happen if there is an error in the catch block?
   • A) It is ignored silently
   • B) It stops program execution
   • C) It triggers another error
   • D) It is caught by the browser’s error handler
9. Which keyword is used to manually throw an error in JavaScript?
   • A) throw
   • B) raise
   • C) error
   • D) halt
10. What should you do if you want to log a custom error message inside a catch block?
    • A) Use console.log with the error message
    • B) Add a finally block with the message
    • C) Use the throw statement
    • D) Write the message in the try block

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Topic: Error Types (SyntaxError, ReferenceError, TypeError)

11. What is a SyntaxError in JavaScript?
    • A) An error due to an invalid syntax in the code
    • B) An error occurring during runtime
    • C) An error caused by incorrect data types
    • D) A logical error in the code
12. When does a ReferenceError typically occur?
    • A) When a variable is not declared or out of scope
    • B) When there is a syntax issue
    • C) When an operation fails
    • D) When accessing invalid object properties
13. Which of these is an example of a TypeError?
    • A) let x = ;
    • B) const a = undefined.a;
    • C) console.log(variable);
    • D) if (x = 10) {}
14. What type of error occurs if you try to assign a value to a constant variable?
    • A) ReferenceError
    • B) SyntaxError
    • C) TypeError
    • D) LogicError
15. What is a common cause of SyntaxError?
    • A) Using a reserved keyword incorrectly
    • B) Using an undefined variable
    • C) Calling a function with wrong parameters
    • D) Accessing a null property
16. Which error will this code throw? console.log(undefinedVariable);
    • A) SyntaxError
    • B) TypeError
    • C) ReferenceError
    • D) None
17. Which error type is associated with attempting to use an object like a function?
    • A) ReferenceError
    • B) SyntaxError
    • C) TypeError
    • D) None
18. Which of the following code snippets will result in a SyntaxError?
    • A) let x = 5;
    • B) if (true {});
    • C) console.log('Hello');
    • D) var y = [];
19. How can you handle a ReferenceError effectively?
    • A) By using the typeof operator to check variable existence
    • B) By rewriting the code
    • C) By adding a finally block
    • D) By avoiding global variables
20. What is the output of console.log(5 + "five");?
    • A) 10
    • B) SyntaxError
    • C) ReferenceError
    • D) 5five

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Topic: Using Console for Debugging

21. Which method logs an object in a table format?
    • A) console.debug
    • B) console.table
    • C) console.log
    • D) console.group
22. What is the use of console.error() in debugging?
    • A) To log errors with stack traces
    • B) To clear the console
    • C) To display information
    • D) To log only syntax errors
23. What is the default log level in console.log()?
    • A) Error
    • B) Debug
    • C) Info
    • D) Warn
24. Which console method stops logging messages until console.groupEnd() is called?
    • A) console.groupCollapsed
    • B) console.pause
    • C) console.error
    • D) console.warn
25. How do you measure the time taken for a block of code using the console?
    • A) console.time and console.timeEnd
    • B) console.start and console.stop
    • C) console.group and console.groupEnd
    • D) console.profile

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Topic: Using Debugger Tools in Browsers

26. What is the purpose of the debugger keyword in JavaScript?
    • A) To throw a debugging exception
    • B) To pause code execution during debugging
    • C) To highlight code errors
    • D) To log variables
27. Which of the following is a browser debugging tool?
    • A) Visual Studio Code
    • B) Chrome DevTools
    • C) Postman
    • D) npm
28. In Chrome DevTools, which tab allows you to set breakpoints?
    • A) Console
    • B) Sources
    • C) Elements
    • D) Network
29. What is the use of a breakpoint in debugging?
    • A) To highlight errors
    • B) To pause execution at a specific line
    • C) To fix runtime issues
    • D) To analyze stack traces
30. How do you inspect variables in real-time using browser debugging tools?
    • A) By using the Network tab
    • B) By hovering over the variable in the Sources tab
    • C) By writing the variable name in the Console tab
    • D) Both B and C

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Answers Table

Qno	Answer
1	B) Defines a block of code to be tested for errors
2	B) Catch
3	C) The catch block is executed
4	B) try { code } catch (error) { handleError }
5	B) To clean up resources regardless of errors
6	B) No, a catch or finally block is required
7	C) Runtime errors
8	C) It triggers another error
9	A) throw
10	A) Use console.log with the error message
11	A) An error due to an invalid syntax in the code
12	A) When a variable is not declared or out of scope
13	B) const a = undefined.a;
14	C) TypeError
15	A) Using a reserved keyword incorrectly
16	C) ReferenceError
17	C) TypeError
18	B) if (true {});
19	A) By using the typeof operator to check variable existence
20	D) 5five
21	B) console.table
22	A) To log errors with stack traces
23	C) Info
24	A) console.groupCollapsed
25	A) console.time and console.timeEnd
26	B) To pause code execution during debugging
27	B) Chrome DevTools
28	B) Sources
29	B) To pause execution at a specific line
30	D) Both B and C