JavaScript Fundamentals

Q1. Which keyword declares a variable in JavaScript?

1. A.variable
2. B.var✓ Correct
3. C.declare
4. D.let

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Q2. What is the correct way to write a single-line comment in JavaScript?

1. A.<!-- comment -->
2. B./* comment */
3. C.// comment✓ Correct
4. D.# comment

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Q3. Which operator is used for strict equality in JavaScript?

1. A.===✓ Correct
2. B.==
3. C.=
4. D.!=

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Q4. What does console.log() do?

1. A.Creates a modal dialog box on screen
2. B.Outputs a message to the browser console✓ Correct
3. C.Logs the user into a website account
4. D.Creates a new log file on disk

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Q5. Which data type represents true or false?

1. A.Number
2. B.Undefined
3. C.String
4. D.Boolean✓ Correct

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Q6. How do you create a function in JavaScript?

1. A.create myFunc() {}
2. B.def myFunc() {}
3. C.func myFunc() {}
4. D.function myFunc() {}✓ Correct

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Q7. What is an array in JavaScript?

1. A.An ordered collection of values✓ Correct
2. B.A type of reusable function
3. C.A single primitive value in memory
4. D.A CSS property declaration

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Q8. How do you write an if statement in JavaScript?

1. A.if (x > 5) {}✓ Correct
2. B.if x > 5 {}
3. C.when (x > 5) {}
4. D.if x > 5 then

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Q9. Which method adds an element to the end of an array?

1. A.add()
2. B.insert()
3. C.append()
4. D.push()✓ Correct

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Q10. What does the typeof operator return?

1. A.The CSS type selector for an HTML element
2. B.A string indicating the data type of a value✓ Correct
3. C.The file type extension of a source file
4. D.The element type in an HTML document

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Q11. What is the difference between let and var?

1. A.var has block scope; let has function scope
2. B.let has block scope; var has function scope✓ Correct
3. C.They are identical in scoping behavior
4. D.let is significantly slower in performance

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Q12. What is a closure in JavaScript?

1. A.A type of loop for iterating over arrays
2. B.A built-in method to end a running program
3. C.A method for closing the browser window
4. D.A function accessing its outer scope variables✓ Correct

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Q13. What is the purpose of the 'this' keyword?

1. A.Refers to the previously declared variable value
2. B.Refers to the current CSS style being applied
3. C.Refers to the object executing current function✓ Correct
4. D.Creates a new object instance in current scope

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Q14. What is hoisting in JavaScript?

1. A.Moving declarations to the top of their scope✓ Correct
2. B.Uploading files from the client to the server
3. C.Raising and throwing runtime error exceptions
4. D.Lifting DOM elements higher in the page layout

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Q15. What is the difference between null and undefined?

1. A.undefined always indicates a runtime error occurred
2. B.They are identical in meaning and behavior
3. C.null is intentional absence; undefined means not assigned✓ Correct
4. D.null is for numbers; undefined is for string values

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Q16. What does the map() method do on an array?

1. A.Creates a geographic map data visualization
2. B.Sorts the array elements in ascending order
3. C.Creates a new array by applying a function to each item✓ Correct
4. D.Maps array indices to their corresponding values

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Q17. What is event bubbling in JavaScript?

1. A.A CSS animation effect using keyframe transitions
2. B.A memory leak issue caused by circular references
3. C.Creating animated bubble visual effects on screen
4. D.When an event on a child propagates up through parents✓ Correct

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Q18. What is the purpose of JSON.parse()?

1. A.Compresses JSON data to reduce its file size
2. B.Creates a new JSON file on the server disk
3. C.Converts a JSON string into a JavaScript object✓ Correct
4. D.Validates JSON syntax for correctness and errors

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Q19. What is template literal syntax in JavaScript?

1. A.Using single quotes around string literals
2. B.Using double quotes around string values
3. C.Using the + operator for concatenation
4. D.Using backticks with ${} for interpolation✓ Correct

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Q20. What is destructuring in JavaScript?

1. A.Permanently deleting JavaScript objects from memory
2. B.Unpacking values from arrays or objects into variables✓ Correct
3. C.Breaking code into smaller modules and files
4. D.Removing DOM elements from the document tree

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Q21. What is the event loop in JavaScript?

1. A.A mechanism handling async callbacks via call stack✓ Correct
2. B.An event listener looping through all DOM elements
3. C.A standard for loop iterating over event arrays
4. D.A DOM traversal method for walking element tree

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Q22. What is the difference between == and === in terms of type coercion?

1. A.Both operators perform type coercion
2. B.Neither operator performs type coercion
3. C.== performs type coercion; === does not✓ Correct
4. D.=== performs type coercion; == does not

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Q23. What is the Temporal Dead Zone (TDZ)?

1. A.A time-related API for scheduling delayed operations
2. B.A concept related to memory management and GC
3. C.A garbage collection phase reclaiming unused memory
4. D.The period between scope entry and let/const declaration✓ Correct

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Q24. What is the difference between call(), apply(), and bind()?

1. A.Only bind invokes the function immediately when called
2. B.call and apply invoke immediately; bind returns a new function✓ Correct
3. C.They are all identical in functionality
4. D.call is for arrays; apply is for objects arguments

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Q25. What is a WeakMap in JavaScript?

1. A.A collection with weakly referenced object keys for GC✓ Correct
2. B.A smaller and more limited version of Map class
3. C.A map collection with weak security encryption
4. D.A map storing only string keys and string values

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Q26. What is the prototype chain in JavaScript?

1. A.A CSS inheritance model for cascading styles
2. B.The mechanism objects use to inherit properties✓ Correct
3. C.A linked list data structure for sequential data
4. D.A blockchain implementation for distributed apps

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Q27. What is tail call optimization in JavaScript?

1. A.A DOM rendering optimization for reducing paint operations
2. B.A CSS optimization technique for faster style calculations
3. C.Optimizing the last element of an array for access
4. D.Reusing the stack frame for a function call in tail position✓ Correct

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Q28. What is the difference between Object.freeze() and Object.seal()?

1. A.freeze prevents all changes; seal allows modifying values✓ Correct
2. B.freeze only prevents deletion of properties
3. C.seal prevents all changes including modifications
4. D.They are identical in behavior on objects

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Q29. What is a Symbol in JavaScript?

1. A.A unique immutable primitive for property identifiers✓ Correct
2. B.A string formatting token for template processing
3. C.A CSS icon or symbol for decorative elements
4. D.A mathematical operator for advanced calculations

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Q30. What is the purpose of generator functions?

1. A.To generate HTML markup from template files
2. B.To create iterators that pause and resume via yield✓ Correct
3. C.To create class instances from constructor functions
4. D.To generate random numbers for cryptographic use

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