JavaScript Objects & Arrays: Concepts and Methods Quiz — Questions & Answers

This quiz contains 16 questions. Below is a complete reference of all questions, answer choices, and correct answers. You can use this section to review after taking the interactive quiz above.

1. Question 1: Object Literal Syntax

   Which of the following is the correct way to define an object literal representing a car with properties 'make' and 'model'?

   • let car = { make: 'Toyota', model: 'Camry' };
   • let car = ( make: 'Toyota', model: 'Camry' );
   • let car = object(make: 'Toyota', model: 'Camry');
   • let car = [ make: 'Toyota', model: 'Camry' ];
   • let car = { make = 'Toyota', model = 'Camry' };
   Show correct answer

   Correct answer: let car = { make: 'Toyota', model: 'Camry' };

2. Question 2: Accessing Object Properties

   Given the object let person = { name: 'Anna', age: 22 }, how can you access the value of 'age'?

   • person(age)
   • person::age
   • person.age
   • person->age
   • person['ages']
   Show correct answer

   Correct answer: person.age

3. Question 3: Adding Object Properties

   How can you add a property 'city' with the value 'London' to an existing object called user?

   • user->city('London');
   • user.city = 'London';
   • user[city] = 'London';
   • user.add('city', 'London');
   • user.city=('London');
   Show correct answer

   Correct answer: user.city = 'London';

4. Question 4: Method Definition in Objects

   What is the correct way to define a method called greet inside an object?

   • greet() => { console.log('Hello'); }
   • greet[] = function() { console.log('Hello'); }
   • function greet() { console.log('Hello'); }
   • greet: function() { console.log('Hello'); }
   • greet = function() { console.log('Hello'); }
   Show correct answer

   Correct answer: greet: function() { console.log('Hello'); }

5. Question 5: The 'this' Keyword Context

   In an object method, what does the 'this' keyword refer to?

   • The function's prototype
   • The parent object
   • The current object calling the method
   • An undefined context
   • The global window object
   Show correct answer

   Correct answer: The current object calling the method

6. Question 6: Prototypal Inheritance

   What does prototypal inheritance in JavaScript allow an object to do?

   • Create private variables
   • Restrict access to methods
   • Inherit properties and methods from another object
   • Compile code at runtime
   • Force strict typing
   Show correct answer

   Correct answer: Inherit properties and methods from another object

7. Question 7: Array map() Method

   If you use the map() method on an array [1, 2, 3] with a function that multiplies each value by 2, what is the resulting array?

   • [3, 2, 1]
   • [2, 2, 2]
   • [1, 2, 3, 6]
   • [1, 4, 9]
   • [2, 4, 6]
   Show correct answer

   Correct answer: [2, 4, 6]

8. Question 8: Array filter() Method

   What will [5, 8, 12, 3].filter(x => x > 6) return?

   • [5, 8]
   • [12, 3]
   • [5, 8, 12]
   • [3, 5, 8, 12]
   • [8, 12]
   Show correct answer

   Correct answer: [8, 12]

9. Question 9: Using Array reduce()

   What does the array method reduce() typically output when called on [1, 2, 3] with (acc, val) => acc + val as the callback?

   • [2, 4, 6]
   • 123
   • 6
   • [1, 2, 3]
   • 1, 2, 3
   Show correct answer

   Correct answer: 6

10. Question 10: Array forEach() Method

    Which statement correctly describes what forEach() does to an array?

    • It calls a provided function once for each array element
    • It reduces the array to a single value
    • It filters the array based on a condition
    • It creates a new array by applying a function
    • It sorts the array in place
    Show correct answer

    Correct answer: It calls a provided function once for each array element

11. Question 11: Array find() Method

    Given let arr = [10, 25, 30]; what does arr.find(x => x > 20) return?

    • [25, 30]
    • undefined
    • 10
    • 25
    • 30
    Show correct answer

    Correct answer: 25

12. Question 12: Object Property Accessors

    Which syntax correctly accesses a property with a key stored in the variable 'prop' from an object 'obj'?

    • obj[prop()]
    • obj.prop
    • obj[prop]
    • obj#prop
    • obj->prop
    Show correct answer

    Correct answer: obj[prop]

13. Question 13: Destructuring Arrays

    How do you use array destructuring to extract the first two values from [7, 8, 9] into variables a and b?

    • let (a, b) = [7, 8];
    • let [a, b] = [7, 8, 9];
    • let {a, b} = [7, 8, 9];
    • let [a b] = [7, 8];
    • let a, b = [7, 8];
    Show correct answer

    Correct answer: let [a, b] = [7, 8, 9];

14. Question 14: Destructuring Objects

    Given const person = { name: 'Kai', age: 30 }, what is the correct way to extract the name property into a variable?

    • const [name] = person;
    • const name = person['names'];
    • const name = { person };
    • const { name } = person;
    • const name = person->name;
    Show correct answer

    Correct answer: const { name } = person;

15. Question 15: Checking Property Existence

    What is the recommended way to check if an object obj has its own property 'id'?

    • obj.exists('id')
    • obj.contains('id')
    • obj.idExist()
    • obj.hasOwnProperty('id')
    • hasProperty(obj, 'id')
    Show correct answer

    Correct answer: obj.hasOwnProperty('id')

16. Question 16: Extending Object Prototypes

    Which statement correctly adds a method speak() to the prototype of a constructor function Animal?

    • Animal.prototype.speak = function() { console.log('Hi'); };
    • Animal->prototype.speak = function() { console.log('Hi'); };
    • Animal::speak = function() { console.log('Hi'); };
    • Animal.prototype:speak = function() { console.log('Hi'); };
    • Animal.speak = function() { console.log('Hi'); };
    Show correct answer

    Correct answer: Animal.prototype.speak = function() { console.log('Hi'); };