MCQs Of Day 19: More Advanced Array Methods
1. What
does the map() method do in JavaScript?
a)
Modifies the original array
b) Returns a new array with transformed values
c) Removes values from the array
d) Iterates through the array without changing it
Answer: b)
Returns a new array with transformed values
Explanation: The map() method applies a transformation to each element
in an array and returns a new array with the results. It doesn't modify the
original array.
2. Which
of the following methods is used to filter an array based on a condition?
a) map()
b) filter()
c) reduce()
d) forEach()
Answer: b)
filter()
Explanation: The filter() method creates a new array with all elements
that pass the test implemented by the provided function.
3. The
reduce() method in JavaScript is used for:
a)
Iterating over an array
b) Filtering out elements
c) Reducing an array to a single value
d) Mapping over elements
Answer: c)
Reducing an array to a single value
Explanation: The reduce() method applies a function against an
accumulator and each element in the array to reduce it to a single value.
4. Which
method is used to execute a function for each element in an array?
a) map()
b) reduce()
c) forEach()
d) filter()
Answer: c)
forEach()
Explanation: The forEach() method executes a provided function once for
each element in the array.
5. What
is the return value of the find() method?
a) A new
array with the found elements
b) The first element that satisfies the condition
c) A boolean indicating if any element matches the condition
d) All elements that match the condition
Answer: b) The
first element that satisfies the condition
Explanation: The find() method returns the first element that matches
the provided condition. If no element matches, it returns undefined.
6. The
some() method in JavaScript checks:
a) If all
elements in an array satisfy a condition
b) If none of the elements in an array satisfy a condition
c) If at least one element in an array satisfies a condition
d) If the array is empty
Answer: c) If at
least one element in an array satisfies a condition
Explanation: The some() method checks if at least one element in the
array satisfies the given condition.
7. Which
method is used to check if all elements in an array satisfy a condition?
a)
every()
b) some()
c) filter()
d) map()
Answer: a)
every()
Explanation: The every() method checks if all elements in the array
satisfy the given condition. It returns true if all elements match, otherwise
false.
8. The
map() method does not modify:
a) The
original array
b) The transformed array
c) The condition applied to elements
d) None of the above
Answer: a) The
original array
Explanation: The map() method returns a new array with the transformed
elements and does not modify the original array.
9. What
will the following code return?
javascript
Copy code
let nums = [1, 2, 3, 4];
let doubled = nums.map(num => num * 2);
console.log(doubled);
a) [2, 4,
6, 8]
b) [1, 4, 9, 16]
c) [2, 4, 6, 8, 10]
d) [1, 2, 3, 4]
Answer: a) [2,
4, 6, 8]
Explanation: The map() method doubles each value in the array, resulting
in [2, 4, 6, 8].
10. Which
of the following is the correct syntax for reduce() method?
a)
array.reduce(callback, initialValue)
b) array.reduce(callback)
c) array.reduce(initialValue, callback)
d) array.reduce()
Answer: a)
array.reduce(callback, initialValue)
Explanation: The reduce() method takes a callback function and an
optional initialValue. The initialValue is used to initialize the accumulator.
11. What
will the following code return?
javascript
Copy code
let arr = [10, 20, 30, 40];
let sum = arr.reduce((acc, num) => acc + num,
0);
console.log(sum);
a) 0
b) 10
c) 100
d) 60
Answer: d) 100
Explanation: The reduce() method calculates the sum of the array
elements: 10 + 20 + 30 + 40 = 100.
12. How
does forEach() differ from map()?
a) forEach()
returns a new array, but map() does not
b) forEach() does not return a new array, but map() does
c) forEach() returns the transformed values, while map() executes a function
d) Both return a new array
Answer: b)
forEach() does not return a new array, but map() does
Explanation: forEach() executes a function for each element but does not
return anything. In contrast, map() returns a new array with transformed
values.
13. Which
of the following methods does NOT modify the original array?
a) map()
b) filter()
c) reduce()
d) All of the above
Answer: d) All
of the above
Explanation: map(), filter(), and reduce() do not modify the original
array; they return a new array or a value.
14. What
will the following code return?
javascript
Copy code
let numbers = [5, 8, 12, 20];
let divisibleByFive = numbers.filter(num => num
% 5 === 0);
console.log(divisibleByFive);
a) [5, 8,
12]
b) [5, 20]
c) [5, 8, 12, 20]
d) []
Answer: b) [5,
20]
Explanation: The filter() method filters out numbers divisible by 5. The
result is [5, 20].
15. What
will find() return if no element satisfies the condition?
a)
undefined
b) null
c) false
d) An empty array
Answer: a)
undefined
Explanation: The find() method returns undefined if no element in the
array satisfies the provided condition.
16. What
will the following code return?
javascript
Copy code
let arr = [1, 2, 3, 4];
let result = arr.find(num => num > 3);
console.log(result);
a) 1
b) 3
c) 4
d) undefined
Answer: c) 4
Explanation: The find() method returns the first element that satisfies
the condition num > 3. Therefore, it returns 4.
17. How
would you check if all numbers in an array are positive?
a) Use
map()
b) Use some()
c) Use every()
d) Use filter()
Answer: c) Use
every()
Explanation: The every() method checks if all elements in the array
satisfy a given condition.
18. What
will the following code return?
javascript
Copy code
let nums = [5, 10, 15, 20];
let result = nums.some(num => num < 10);
console.log(result);
a) true
b) false
c) undefined
d) null
Answer: a) true
Explanation: The some() method checks if any element in the array is
less than 10. Since 5 satisfies the condition, it returns true.
19. Which
method returns a boolean value based on a condition?
a) map()
b) filter()
c) reduce()
d) some()
Answer: d)
some()
Explanation: The some() method returns true if at least one element
satisfies the condition, otherwise it returns false.
20. What
does map() return?
a) A
boolean
b) A new array with modified elements
c) A single transformed value
d) undefined
Answer: b) A new
array with modified elements
Explanation: The map() method returns a new array with the values
transformed by the provided function.
21. What
will be the result of the following code?
javascript
Copy code
let nums = [1, 2, 3];
let newNums = nums.map(num => num * 2);
console.log(newNums);
a) [1, 2,
3]
b) [2, 4, 6]
c) [1, 4, 9]
d) [2, 4, 6, 8]
Answer: b) [2,
4, 6]
Explanation: The map() method multiplies each element by 2, resulting in
[2, 4, 6].
22. Which
of the following array methods does not return a new array?
a) map()
b) reduce()
c) filter()
d) slice()
Answer: b)
reduce()
Explanation: The reduce() method reduces an array to a single value, not
an array.
23. What
is the initial value used in the reduce() method?
a) It is
always 0
b) It is provided as the second argument to the reduce() method
c) It is calculated by the browser automatically
d) It is undefined
Answer: b) It is
provided as the second argument to the reduce() method
Explanation: The second argument of reduce() is the initial value for
the accumulator. If not provided, the first element of the array is used.
24. What
will the following code output?
javascript
Copy code
let nums = [10, 20, 30, 40];
let result = nums.reduce((acc, num) => acc +
num, 100);
console.log(result);
a) 100
b) 200
c) 300
d) 150
Answer: d) 150
Explanation: The reduce() method starts with an accumulator value of
100, and adds each element: 100 + 10 + 20 + 30 + 40 = 150.
25. What
will the following code return?
javascript
Copy code
let arr = [1, 2, 3, 4];
let result = arr.map(x => x + 2);
console.log(result);
a) [1, 2,
3, 4]
b) [3, 4, 5, 6]
c) [2, 4, 6, 8]
d) [1, 2, 3]
Answer: b) [3,
4, 5, 6]
Explanation: The map() method adds 2 to each element of the array,
resulting in [3, 4, 5, 6].
I'll
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Here are
the remaining 75 multiple-choice questions (MCQs) on advanced array methods in
JavaScript with explanations:
26. What
does the splice() method do in JavaScript?
a)
Removes elements from an array
b) Adds elements to an array
c) Both removes and adds elements to an array
d) Creates a shallow copy of the array
Answer: c) Both
removes and adds elements to an array
Explanation: The splice() method can remove, replace, or add elements in
an array at a specific position.
27. Which
of the following methods changes the original array?
a) map()
b) filter()
c) forEach()
d) splice()
Answer: d)
splice()
Explanation: The splice() method modifies the original array by removing
or adding elements.
28. Which
method would you use to check if an array contains a specific value?
a)
includes()
b) indexOf()
c) find()
d) some()
Answer: a)
includes()
Explanation: The includes() method checks if an array contains a
specific value and returns true or false.
29. Which
of the following methods can be used to combine multiple arrays into one?
a)
concat()
b) join()
c) map()
d) slice()
Answer: a)
concat()
Explanation: The concat() method is used to combine two or more arrays
into a single array.
30. What
does the sort() method do in JavaScript?
a) Sorts
an array in ascending order by default
b) Sorts an array in descending order by default
c) Sorts an array based on the given criteria
d) Sorts the elements in the order they appear
Answer: a) Sorts
an array in ascending order by default
Explanation: The sort() method sorts the elements of an array in
ascending order by default (as strings).
31. How
does join() work in JavaScript?
a) Joins
elements of an array into a string
b) Combines two arrays
c) Splits a string into an array
d) Adds an element at the end of the array
Answer: a) Joins
elements of an array into a string
Explanation: The join() method joins all elements of an array into a
single string, with an optional separator.
32. What
does the shift() method do in JavaScript?
a) Adds
an element at the beginning of an array
b) Removes the last element of an array
c) Removes the first element of an array
d) Sorts the array in ascending order
Answer: c)
Removes the first element of an array
Explanation: The shift() method removes the first element of an array
and returns it.
33. What
does the unshift() method do in JavaScript?
a)
Removes the first element of the array
b) Adds one or more elements to the beginning of an array
c) Removes the last element of the array
d) Adds one or more elements to the end of an array
Answer: b) Adds
one or more elements to the beginning of an array
Explanation: The unshift() method adds one or more elements to the
beginning of an array and returns the new length of the array.
34. Which
method is used to create a shallow copy of an array?
a) copy()
b) slice()
c) clone()
d) map()
Answer: b)
slice()
Explanation: The slice() method creates a shallow copy of a portion of
an array and returns it.
35. What
will be the output of the following code?
javascript
Copy code
let arr = [1, 2, 3, 4];
let copy = arr.slice();
console.log(copy);
a) [1, 2,
3, 4]
b) undefined
c) [2, 3, 4]
d) []
Answer: a) [1,
2, 3, 4]
Explanation: The slice() method creates a shallow copy of the array, so
copy will be [1, 2, 3, 4].
36. Which
method would you use to extract a portion of an array without modifying the
original array?
a)
splice()
b) slice()
c) shift()
d) pop()
Answer: b)
slice()
Explanation: The slice() method extracts a portion of an array without
modifying the original array.
37. How does
the reverse() method work in JavaScript?
a)
Reverses the order of elements in an array
b) Sorts the array in reverse order
c) Reverses the string values inside an array
d) Reverses the values based on a condition
Answer: a)
Reverses the order of elements in an array
Explanation: The reverse() method reverses the order of elements in an
array, modifying the original array.
38. Which
of the following methods removes the last element from an array?
a)
shift()
b) pop()
c) unshift()
d) splice()
Answer: b) pop()
Explanation: The pop() method removes the last element from an array and
returns it.
39. Which
of the following is true about the forEach() method?
a) It
creates a new array
b) It returns a boolean value
c) It executes a provided function for each array element
d) It modifies the original array
Answer: c) It
executes a provided function for each array element
Explanation: The forEach() method calls a function for each element in
the array but does not return anything.
40. Which
array method would you use to check the index of a specific value in an array?
a)
indexOf()
b) findIndex()
c) includes()
d) map()
Answer: a)
indexOf()
Explanation: The indexOf() method returns the first index of the
specified value or -1 if not found.
41. What
is the return value of find() when no elements match the condition?
a) null
b) undefined
c) false
d) 0
Answer: b)
undefined
Explanation: The find() method returns undefined if no element in the
array satisfies the given condition.
42. What
is the purpose of the concat() method?
a) To
remove elements from an array
b) To add new elements to an array
c) To join two or more arrays
d) To modify the existing array
Answer: c) To
join two or more arrays
Explanation: The concat() method is used to merge two or more arrays
into one array.
43. What
will the following code return?
javascript
Copy code
let arr = [1, 2, 3, 4];
let result = arr.indexOf(3);
console.log(result);
a) 2
b) 3
c) 1
d) undefined
Answer: a) 2
Explanation: The indexOf() method returns the index of the first
occurrence of 3, which is 2.
44. Which
method is used to sort an array in descending order?
a)
reverse()
b) sort()
c) sort((a, b) => b - a)
d) reverse().sort()
Answer: c)
sort((a, b) => b - a)
Explanation: The sort() method can be used with a custom comparison
function to sort in descending order.
45. What
will the following code return?
javascript
Copy code
let arr = [5, 4, 3, 2, 1];
let sortedArr = arr.sort((a, b) => b - a);
console.log(sortedArr);
a) [1, 2,
3, 4, 5]
b) [5, 4, 3, 2, 1]
c) [5, 3, 2, 1, 4]
d) [4, 5, 1, 3, 2]
Answer: b) [5,
4, 3, 2, 1]
Explanation: The sort() method sorts the array in descending order based
on the custom comparator (a, b) => b - a.
46. What
will be the output of the following code?
javascript
Copy code
let arr = ['apple', 'banana', 'cherry'];
let result = arr.join('-');
console.log(result);
a) apple
banana cherry
b) apple,banana,cherry
c) apple-banana-cherry
d) undefined
Answer: c)
apple-banana-cherry
Explanation: The join() method joins the array elements into a string
with the specified separator ('-' in this case).
47. What
is the time complexity of the map() method?
a) O(1)
b) O(n)
c) O(n^2)
d) O(log n)
Answer: b) O(n)
Explanation: The map() method iterates through all elements in the
array, resulting in a time complexity of O(n), where n is the number of
elements.
48. What
is the some() method used for?
a) To
check if all elements in the array pass the test
b) To check if at least one element passes the test
c) To modify the elements of an array
d) To return an array of modified elements
Answer: b) To
check if at least one element passes the test
Explanation: The some() method tests if at least one element in the
array satisfies the provided condition and returns true or false.
I'll
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Here are
more multiple-choice questions (MCQs) with explanations:
49. Which
of the following methods is used to transform an array into a single value?
a) map()
b) reduce()
c) filter()
d) forEach()
Answer: b)
reduce()
Explanation: The reduce() method processes each element of the array and
accumulates the result into a single value (e.g., sum, product).
50. What
will the following code return?
javascript
Copy code
let arr = [10, 20, 30, 40];
let result = arr.reduce((acc, curr) => acc +
curr, 0);
console.log(result);
a) 100
b) 30
c) 60
d) undefined
Answer: a) 100
Explanation: The reduce() method sums the values in the array, starting
from the initial value 0. So, 10 + 20 + 30 + 40 = 100.
51. Which
array method is used to test if all elements in the array satisfy a given
condition?
a)
every()
b) some()
c) find()
d) forEach()
Answer: a)
every()
Explanation: The every() method tests whether all elements in the array
satisfy a given condition. It returns true if all elements pass the test.
52. What
does the find() method return when no element matches the condition?
a) null
b) undefined
c) false
d) 0
Answer: b)
undefined
Explanation: The find() method returns undefined if no element in the
array satisfies the given condition.
53. What
is the difference between some() and every() methods?
a) some()
tests if at least one element satisfies the condition, while every() tests if
all elements satisfy the condition.
b) some() tests if all elements satisfy the condition, while every() tests if
at least one element satisfies the condition.
c) some() returns a new array, while every() returns a boolean.
d) some() does not work with arrays, while every() does.
Answer: a)
some() tests if at least one element satisfies the condition, while every()
tests if all elements satisfy the condition.
Explanation: The some() method checks if at least one element meets the
condition, and the every() method checks if every element meets the condition.
54. How
does the map() method work in JavaScript?
a) It
filters out elements from an array
b) It transforms each element in an array
c) It modifies the original array
d) It removes all non-numeric values from the array
Answer: b) It
transforms each element in an array
Explanation: The map() method creates a new array by applying a given
function to each element of the original array without modifying the original
array.
55. Which
of the following methods creates a shallow copy of an array?
a) map()
b) forEach()
c) slice()
d) reduce()
Answer: c)
slice()
Explanation: The slice() method creates a shallow copy of a portion or
the entire array.
56. Which
method is used to create a new array by including only the elements that
satisfy a given condition?
a) map()
b) filter()
c) reduce()
d) forEach()
Answer: b)
filter()
Explanation: The filter() method creates a new array with all elements
that pass a test (provided by a function).
57. What
will the following code return?
javascript
Copy code
let arr = [1, 2, 3, 4];
let result = arr.map(x => x * 2);
console.log(result);
a) [2, 4,
6, 8]
b) [1, 2, 3, 4]
c) [2, 3, 4, 5]
d) [4, 6, 8, 10]
Answer: a) [2,
4, 6, 8]
Explanation: The map() method transforms each element of the array by
multiplying it by 2.
58. What
will be the output of the following code?
javascript
Copy code
let arr = [10, 20, 30, 40];
let result = arr.filter(x => x > 20);
console.log(result);
a) [10,
20]
b) [30, 40]
c) [20, 30, 40]
d) [10, 30, 40]
Answer: b) [30,
40]
Explanation: The filter() method creates a new array containing elements
greater than 20 (30 and 40).
59. How
does the forEach() method differ from map()?
a)
forEach() returns a new array, while map() does not
b) forEach() executes a function for each element, but map() modifies the
original array
c) forEach() does not return a value, while map() returns a new array
d) forEach() creates a shallow copy of the array, while map() modifies the
original array
Answer: c)
forEach() does not return a value, while map() returns a new array
Explanation: The forEach() method does not return anything, whereas
map() creates and returns a new array with the transformed values.
60. What
will the following code output?
javascript
Copy code
let arr = [10, 20, 30, 40];
let result = arr.reduce((acc, curr) => acc -
curr, 100);
console.log(result);
a) 60
b) 50
c) 40
d) 30
Answer: b) 50
Explanation: The reduce() method starts with an initial value of 100 and
subtracts each element in the array from it, resulting in 100 - 10 - 20 - 30 -
40 = 50.
61. Which
method is used to check if an array contains a specific element?
a)
contains()
b) find()
c) indexOf()
d) includes()
Answer: d)
includes()
Explanation: The includes() method checks if a given element exists in
the array and returns true or false.
62. Which
method is used to combine two arrays?
a) join()
b) concat()
c) add()
d) merge()
Answer: b)
concat()
Explanation: The concat() method combines two or more arrays into one
new array.
63. What
will the following code return?
javascript
Copy code
let arr = [1, 2, 3];
let result = arr.reduce((acc, curr) => acc *
curr, 1);
console.log(result);
a) 6
b) 3
c) 0
d) 1
Answer: a) 6
Explanation: The reduce() method multiplies all elements in the array
starting with an initial value of 1, resulting in 1 * 2 * 3 = 6.
64. What
is the output of the following code?
javascript
Copy code
let arr = [1, 2, 3, 4];
let result = arr.find(x => x > 2);
console.log(result);
a) 1
b) 2
c) 3
d) undefined
Answer: c) 3
Explanation: The find() method returns the first element that satisfies
the condition, in this case, the first element greater than 2, which is 3.
65. What
does the sort() method do by default?
a) Sorts
an array in ascending order
b) Sorts an array in descending order
c) Sorts the array as per the function passed
d) Does not sort the array
Answer: a) Sorts
an array in ascending order
Explanation: The sort() method, by default, sorts the array elements in
ascending order as strings.
66. What
is the time complexity of map()?
a) O(n)
b) O(n^2)
c) O(1)
d) O(log n)
Answer: a) O(n)
Explanation: The map() method iterates through the array and applies a
transformation function to each element, so its time complexity is O(n).
I'll
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said:
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Here are
the remaining MCQs continuing from the previous list:
67. What
is the result of the following code?
javascript
Copy code
let arr = [1, 2, 3, 4];
let result = arr.some(x => x > 3);
console.log(result);
a) false
b) true
c) undefined
d) NaN
Answer: b) true
Explanation: The some() method checks if at least one element satisfies
the condition (x > 3). Since 4 satisfies the condition, it returns true.
68. Which
method is used to iterate over an array and call a provided function once for
each array element?
a) forEach()
b) map()
c) reduce()
d) filter()
Answer: a)
forEach()
Explanation: The forEach() method executes a provided function once for
each array element, without returning a new array.
69. What
will be the output of the following code?
javascript
Copy code
let arr = [1, 2, 3];
let result = arr.map(x => x ** 2);
console.log(result);
a) [1, 2,
3]
b) [1, 4, 9]
c) [2, 4, 6]
d) [1, 2, 3, 4]
Answer: b) [1,
4, 9]
Explanation: The map() method transforms each element of the array by
squaring them (x ** 2), resulting in [1, 4, 9].
70. What
is the time complexity of the forEach() method?
a) O(n)
b) O(log n)
c) O(1)
d) O(n^2)
Answer: a) O(n)
Explanation: The forEach() method processes each element of the array
one by one, resulting in a time complexity of O(n), where n is the number of
elements in the array.
71. What
will the following code output?
javascript
Copy code
let arr = [1, 2, 3, 4];
let result = arr.every(x => x > 0);
console.log(result);
a) false
b) true
c) undefined
d) NaN
Answer: b) true
Explanation: The every() method tests if every element satisfies the
condition (x > 0). Since all elements in the array are greater than 0, it
returns true.
72. How
does the find() method behave if multiple elements match the condition?
a) It
returns the last matching element.
b) It returns the first matching element.
c) It throws an error.
d) It returns all matching elements.
Answer: b) It
returns the first matching element.
Explanation: The find() method returns the first element that satisfies
the provided condition, even if there are multiple matches.
73. What
will be the output of the following code?
javascript
Copy code
let arr = [1, 2, 3, 4];
let result = arr.filter(x => x < 3);
console.log(result);
a) [1, 2,
3]
b) [1, 2]
c) [3, 4]
d) [4]
Answer: b) [1,
2]
Explanation: The filter() method creates a new array with elements less
than 3, resulting in [1, 2].
74. Which
method will return a new array containing only the elements that satisfy a
given condition?
a) map()
b) filter()
c) some()
d) forEach()
Answer: b)
filter()
Explanation: The filter() method creates a new array with all the
elements that pass a test (condition).
75. Which
of the following methods can be used to add elements to the beginning of an
array?
a) push()
b) pop()
c) unshift()
d) shift()
Answer: c)
unshift()
Explanation: The unshift() method adds one or more elements to the
beginning of an array, changing its length.
76. What
will be the output of the following code?
javascript
Copy code
let arr = [5, 10, 15, 20];
let result = arr.map(x => x / 5);
console.log(result);
a) [1, 2,
3, 4]
b) [5, 10, 15, 20]
c) [0.2, 0.4, 0.6, 0.8]
d) [0, 1, 2, 3]
Answer: a) [1,
2, 3, 4]
Explanation: The map() method divides each element by 5, resulting in
[1, 2, 3, 4].
77. Which
method is used to check whether at least one element in an array satisfies a
condition?
a) some()
b) every()
c) map()
d) reduce()
Answer: a)
some()
Explanation: The some() method checks if at least one element satisfies
the condition. It returns true if any one element passes the condition.
78. What
will the following code return?
javascript
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let arr = [10, 20, 30, 40];
let result = arr.reduce((acc, curr) => acc *
curr, 1);
console.log(result);
a) 24000
b) 100
c) 400
d) 30
Answer: a) 24000
Explanation: The reduce() method multiplies all elements starting with
an initial value of 1, so 1 * 10 * 20 * 30 * 40 = 24000.
79. How
can you modify the values in an array without changing the original array?
a) Use
map()
b) Use filter()
c) Use reduce()
d) Use forEach()
Answer: a) Use
map()
Explanation: The map() method transforms the elements of an array and
returns a new array, without modifying the original array.
80. What
will be the output of the following code?
javascript
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let arr = [1, 2, 3, 4];
let result = arr.reduce((acc, curr) => acc +
curr, 10);
console.log(result);
a) 20
b) 30
c) 40
d) 50
Answer: b) 30
Explanation: The reduce() method starts with an initial value of 10,
then adds each element in the array: 10 + 1 + 2 + 3 + 4 = 30.
81. Which
of the following methods does NOT modify the original array?
a)
splice()
b) sort()
c) map()
d) push()
Answer: c) map()
Explanation: The map() method creates a new array and does not modify
the original array.
82. Which
method can be used to create a string from the elements of an array?
a) join()
b) concat()
c) reduce()
d) split()
Answer: a)
join()
Explanation: The join() method combines all elements of the array into a
single string.
83. What
will the following code return?
javascript
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let arr = [10, 20, 30, 40];
let result = arr.find(x => x === 30);
console.log(result);
a) 20
b) 30
c) undefined
d) NaN
Answer: b) 30
Explanation: The find() method returns the first element that matches
the condition (x === 30), which is 30.
84. What
is the time complexity of filter()?
a) O(1)
b) O(n)
c) O(n^2)
d) O(log n)
Answer: b) O(n)
Explanation: The filter() method iterates through all elements of the
array, resulting in a time complexity of O(n).
85. What
will the following code output?
javascript
Copy code
let arr = [5, 10, 15, 20];
let result = arr.filter(x => x > 10);
console.log(result);
a) [5,
10]
b) [15, 20]
c) [10, 15, 20]
d) [5, 15, 20]
Answer: b) [15,
20]
Explanation: The filter() method creates a new array containing the
elements greater than 10, resulting in [15, 20].
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Here are
more MCQs on the topics of advanced array methods:
86. What
will the following code return?
javascript
Copy code
let arr = [5, 10, 15, 20];
let result = arr.reduce((acc, curr) => acc -
curr, 0);
console.log(result);
a) -40
b) -30
c) 40
d) 30
Answer: b) -30
Explanation: The reduce() method starts with an initial value of 0. The
calculation proceeds as 0 - 5 - 10 - 15 - 20, resulting in -30.
87. Which
method allows you to apply a function to each element of an array and return a
new array with the results?
a)
forEach()
b) map()
c) filter()
d) every()
Answer: b) map()
Explanation: The map() method creates a new array by applying a function
to each element of the array.
88. How
would you find whether an element exists in an array using a callback function?
a) some()
b) find()
c) filter()
d) reduce()
Answer: a)
some()
Explanation: The some() method checks if at least one element satisfies
the provided condition and returns true if it does.
89. Which
method would you use to create a string by concatenating all elements of an
array, separated by a comma?
a) join()
b) concat()
c) reduce()
d) split()
Answer: a)
join()
Explanation: The join() method joins all elements of the array into a
single string with a specified separator, defaulting to a comma.
90. Which
method would you use to transform each item in an array into a new value
without modifying the original array?
a)
forEach()
b) map()
c) filter()
d) reduce()
Answer: b) map()
Explanation: The map() method applies a function to each item of an
array and returns a new array with transformed values.
91. What
will be the output of the following code?
javascript
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let arr = [2, 4, 6];
let result = arr.reduce((acc, curr) => acc + curr,
1);
console.log(result);
a) 13
b) 12
c) 15
d) 14
Answer: a) 13
Explanation: The reduce() method starts with an initial value of 1, so
the calculation proceeds as 1 + 2 + 4 + 6 = 13.
92. What
does the every() method return when applied to an array where all elements
satisfy a condition?
a) false
b) true
c) undefined
d) NaN
Answer: b) true
Explanation: The every() method returns true if all elements in the
array satisfy the provided condition.
93. What
is the return value of the find() method if no element matches the condition?
a) null
b) undefined
c) false
d) NaN
Answer: b)
undefined
Explanation: If no element in the array satisfies the condition, the
find() method returns undefined.
94. Which
of the following methods would be used to apply a function to each element of
an array, but it doesn't return a new array?
a) map()
b) reduce()
c) forEach()
d) filter()
Answer: c)
forEach()
Explanation: The forEach() method executes a function for each element
in the array but does not return a new array.
95. What
is the output of the following code?
javascript
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let arr = [2, 4, 6, 8];
let result = arr.some(x => x > 6);
console.log(result);
a) false
b) true
c) undefined
d) NaN
Answer: b) true
Explanation: The some() method checks if at least one element satisfies
the condition (x > 6). Since 8 is greater than 6, it returns true.
96. Which
method is used to accumulate all the elements in an array into a single value?
a) map()
b) reduce()
c) filter()
d) some()
Answer: b)
reduce()
Explanation: The reduce() method accumulates all elements in an array
into a single value based on the provided callback function.
97. What
will the following code output?
javascript
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let arr = [1, 2, 3, 4];
let result = arr.filter(x => x > 2);
console.log(result);
a) [1, 2]
b) [3, 4]
c) [2, 3, 4]
d) [4]
Answer: b) [3,
4]
Explanation: The filter() method returns elements greater than 2, which
are 3 and 4.
98. Which
method would you use to check if all elements in an array pass a test?
a)
forEach()
b) some()
c) map()
d) every()
Answer: d)
every()
Explanation: The every() method checks if all elements in an array
satisfy a condition.
99. What
will the following code output?
javascript
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let arr = [1, 2, 3, 4];
let result = arr.map(x => x * 2).filter(x =>
x > 5);
console.log(result);
a) [2, 4,
6, 8]
b) [6, 8]
c) [1, 2, 3, 4]
d) [10, 12]
Answer: b) [6,
8]
Explanation: The map() method doubles each element, resulting in [2, 4,
6, 8], and then the filter() method keeps elements greater than 5, which are 6
and 8.
100.
Which of the following methods is used to add one or more elements to the end
of an array?
a) push()
b) shift()
c) unshift()
d) pop()
Answer: a)
push()
Explanation: The push() method adds one or more elements to the end of
an array, modifying the original array.
