JavaScript objects are commonly defined using an object literal, which is a list of name:value pairs inside curly braces.
2. What are the properties of a JavaScript object?
a) Functions inside an object
b) The data values associated with an object
c) The methods available to an object
d) The parameters passed to an object
Answer:
b) The data values associated with an object
Explanation:
The properties of a JavaScript object are the data values associated with it, defined as name:value pairs.
3. How can you access the properties of a JavaScript object?
a) Using square brackets []
b) Through dot notation or square brackets
c) By calling a method on the object
d) By using the new keyword
Answer:
b) Through dot notation or square brackets
Explanation:
Properties of a JavaScript object can be accessed either through dot notation (objectName.propertyName) or square brackets (objectName["propertyName"]).
4. What is a method in a JavaScript object?
a) A variable that stores data
b) A function stored as a property
c) A standalone function
d) A prototype of the object
Answer:
b) A function stored as a property
Explanation:
Methods in JavaScript objects are actions that can be performed on objects. They are essentially functions stored as properties within the object.
5. In JavaScript, what does the this keyword refer to inside an object method?
a) The global object
b) The nearest function
c) The object itself
d) The window object
Answer:
c) The object itself
Explanation:
Inside an object method, the this keyword refers to the object itself, allowing access to its properties and methods.
6. What happens if you access an object method without parentheses in JavaScript?
a) The method is deleted
b) The method is invoked
c) It returns the function definition
d) It returns undefined
Answer:
c) It returns the function definition
Explanation:
Accessing an object method without parentheses returns the function definition of the method, rather than executing it.
7. Why should you avoid declaring Strings, Numbers, and Booleans as Objects in JavaScript?
a) It is not allowed in JavaScript
b) It complicates the code and slows down execution speed
c) It changes the value type to 'undefined'
d) It automatically converts them to arrays
Answer:
b) It complicates the code and slows down execution speed
Explanation:
Declaring Strings, Numbers, and Booleans as objects is discouraged as it complicates the code and can slow down execution speed.
8. What is a key feature of JavaScript objects?
a) They can only store numerical values
b) They are used to store key/value collections
c) They cannot have methods
d) They are immutable
Answer:
b) They are used to store key/value collections
Explanation:
JavaScript objects are used to store collections of data as key/value pairs, making them versatile for various data structures.
9. What does the constructor property of a JavaScript object return?
a) The value of the object
b) The function that created the object's prototype
c) The number of properties in the object
d) The string representation of the object
Answer:
b) The function that created the object's prototype
Explanation:
The constructor property of a JavaScript object returns the function that created the object's prototype.
10. How do you retrieve all the keys of a JavaScript object as an array?
a) Using the values() method
b) Using the keys() method
c) Through the length property
d) With the forEach() method
Answer:
b) Using the keys() method
Explanation:
The keys() method returns an Array Iterator object with the keys of the object, allowing you to iterate over the keys.
11. What is the purpose of the prototype property in JavaScript objects?
a) To check if an object is a prototype of another
b) To return the string representation of an object
c) To add properties and methods to an object
d) To create a new instance of an object
Answer:
c) To add properties and methods to an object
Explanation:
The prototype property allows you to add new properties and methods to existing object types.
12. What does the toString() method do when called on a JavaScript object?
a) It returns the type of the object
b) It converts the object to its string representation
c) It returns the values of the object as a string
d) It checks if the object is converted to a string
Answer:
b) It converts the object to its string representation
Explanation:
The toString() method is used to convert an object to a string and return the result.
13. How does the valueOf() method of a JavaScript object work?
a) It changes the values of the object
b) It returns the primitive value of the object
c) It sets the value of the object
d) It returns the string representation of the object
Answer:
b) It returns the primitive value of the object
Explanation:
The valueOf() method is used to return the primitive value of a JavaScript object.
14. What is the best practice for declaring JavaScript objects?
a) Using the var keyword
b) Using the let keyword
c) Using the new keyword
d) Using the const keyword
Answer:
d) Using the const keyword
Explanation:
It is a common practice to declare objects with the const keyword to prevent them from being reassigned.
15. How are object methods in JavaScript defined?
a) As separate functions outside the object
b) As function expressions assigned to properties
c) Using the new keyword
d) By using square brackets
Answer:
b) As function expressions assigned to properties
Explanation:
Object methods in JavaScript are defined as function expressions that are assigned to properties within the object.