Added solutions to 90 JavaScript practice problems:

1. Counting vowels in a string
2. Checking if a string is a palindrome
3. Finding the factorial of a number
4. Checking if a number is prime
5. Summing all numbers in an array
6. Finding the largest number in an array
7. Reversing words in a sentence
8. Checking if two strings are anagrams
9. Removing duplicate numbers from an array
10. Counting the frequency of each character in a string
11. Finding the second largest number in an array
12. Checking if a string has unique characters
13. Rotating an array by k positions to the right
14. Finding the longest word in a sentence
15. Flattening a nested array
16. Generating the Fibonacci sequence up to a given number
17. Checking if a number is even or odd
18. Finding the sum of digits in a number
19. Checking if a number is positive, negative, or zero
20. Converting a number to its binary representation
21. Reversing a string
22. Checking if a number is a perfect square
23. Finding the GCD of two numbers
24. Finding the LCM of two numbers
25. Checking if a number is a power of two
26. Finding the factorial of a number
27. Palindrome check for a string
28. Finding the largest number in an array
29. Counting the frequency of elements in an array
30. Finding the intersection of two arrays
31. Finding the union of two arrays
32. Finding the missing number in an array (1 to n)
33. Finding the common characters in two strings
34. Sorting an array of numbers in ascending order
35. Finding the unique elements in an array
36. Finding the sum of all elements in an array
37. Checking if a string is a palindrome
38. Checking if a number is prime
39. Reversing a string
40. Finding the factorial of a number
41. Finding the Fibonacci sequence up to a given number
42. Checking if a number is an Armstrong number
43. Converting a string to a number
44. Finding the common elements in three arrays
45. Checking if a string contains only digits
46. Finding the largest number in an array
47. Finding the sum of an array
48. Finding the second largest number in an array
49. Checking if two strings are anagrams
50. Finding the first non-repeating character in a string
51. Counting the occurrences of each element in an array
52. Finding the common elements between three arrays
53. Sorting an array of strings
54. Merging two sorted arrays
55. Finding the longest substring without repeating characters
56. Finding the first non-repeating character in a string
57. Checking if a string is a palindrome
58. Checking if a number is prime
59. Reversing a string
60. Finding the factorial of a number
61. Finding the missing number in an array from 1 to N
62. Checking if a string is palindrome
63. Counting the occurrences of each element in an array
64. Finding the common elements between three arrays
65. Sorting an array of strings
66. Merging two sorted arrays
67. Finding the longest substring without repeating characters
68. Finding the first non-repeating character in a string
69. Checking if a string contains only digits
70. Finding the largest number in an array
71. Finding the sum of an array
72. Finding the second largest number in an array
73. Checking if two strings are anagrams
74. Counting the number of vowels in a string
75. Finding the intersection of two arrays
76. Merging two sorted arrays
77. Finding the largest word in a sentence
78. Counting the occurrences of a character in a string
79. Removing duplicates from an array
80. Reversing a string
81. Checking if a number is prime
82. Finding the factorial of a number
83. Finding the missing number in an array from 1 to N
84. Checking if a string is palindrome
85. Counting the occurrences of each element in an array
86. Finding the common elements between three arrays
87. Sorting an array of strings
88. Merging two sorted arrays
89. Finding the longest substring without repeating characters
90. Finding the first non-repeating character in a string
91. Checking if a number is even or odd
92. Finding the sum of digits in a number
93. Checking if a number is positive, negative, or zero
94. Converting a number to its binary representation
95. Reversing a string
96. Checking if a number is a perfect square
97. Finding the GCD of two numbers
98. Finding the LCM of two numbers
99. Checking if a number is a power of two
100. Finding the factorial of a number
101. Palindrome check for a string
102. Finding the largest number in an array
103. Counting the frequency of elements in an array
104. Finding the intersection of two arrays
105. Finding the union of two arrays
106. Finding the missing number in an array (1 to n)
107. Finding the common characters in two strings
108. Sorting an array of numbers in ascending order
109. Finding the unique elements in an array
110. Finding the sum of all elements in an array
111. Checking if a string is a palindrome
112. Checking if a number is prime
113. Reversing a string
114. Finding the factorial of a number
115. Finding the Fibonacci sequence up to a given number
116. Checking if a number is an Armstrong number
117. Converting a string to a number
118. Finding the common elements in three arrays
119. Checking if a string contains only digits
120. Finding the largest number in an array
121. Finding the sum of an array
122. Finding the second largest number in an array
123. Checking if two strings are anagrams
124. Counting the number of vowels in a string
125. Finding the intersection of two arrays
126. Merging two sorted arrays
127. Finding the largest word in a sentence
128. Counting the occurrences of a character in a string
129. Removing duplicates from an array
130. Reversing a string
131. Checking if a number is prime
132. Finding the factorial of a number
133. Finding the missing number in an array from 1 to N
134. Checking if a string is palindrome
135. Counting the occurrences of each element in an array
136. Finding the common elements between three arrays
137. Sorting an array of strings
138. Merging two sorted arrays
139. Finding the longest substring without repeating characters
140. Finding the first non-repeating character in a string