# JavaScript functions - Exercises, Practice, Solution

## JavaScript functions [29 exercises with solution]

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1. Write a JavaScript function that reverses a number.
Example x = 32243;
Expected Output : 34223
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2. Write a JavaScript function that checks whether a passed string is a palindrome or not?
A palindrome is word, phrase, or sequence that reads the same backward as forward, e.g., madam or nurses run.
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3. Write a JavaScript function that generates all combinations of a string.
Example string : 'dog'
Expected Output : d,do,dog,o,og,g
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4. Write a JavaScript function that returns a string that has letters in alphabetical order.
Example string : 'webmaster'
Expected Output : 'abeemrstw'
Assume punctuation and numbers symbols are not included in the passed string.
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5. Write a JavaScript function that accepts a string as a parameter and converts the first letter of each word into upper case.
Example string : 'the quick brown fox'
Expected Output : 'The Quick Brown Fox '
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6. Write a JavaScript function that accepts a string as a parameter and finds the longest word within the string.
Example string : 'Web Development Tutorial'
Expected Output : 'Development'
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7. Write a JavaScript function that accepts a string as a parameter and counts the number of vowels within the string.
Note : As the letter 'y' can be regarded as both a vowel and a consonant, we do not count 'y' as vowel here.
Example string : 'The quick brown fox'
Expected Output : 5
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8. Write a JavaScript function that accepts a number as a parameter and checks whether it is prime or not.
Note : A prime number (or a prime) is a natural number greater than 1 that has no positive divisors other than 1 and itself.
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9. Write a JavaScript function that accepts an argument and returns the type.
Note : There are six possible values that typeof returns: object, boolean, function, number, string, and undefined.
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10. Write a JavaScript function which returns the n rows by n columns identity matrix.
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11. Write a JavaScript function that takes an array of numbers and finds the second lowest and second greatest numbers, respectively.
Sample array : [1,2,3,4,5]
Expected Output : 2,4
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12. Write a JavaScript function that checks whether a number is perfect.
According to Wikipedia : In number theory, a perfect number is a positive integer that is equal to the sum of its proper positive divisors, that is, the sum of its positive divisors excluding the number itself (also known as its aliquot sum). Equivalently, a perfect number is a number that is half the sum of all of its positive divisors (including itself).
Example : The first perfect number is 6, because 1, 2, and 3 are its proper positive divisors, and 1 + 2 + 3 = 6. Equivalently, the number 6 is equal to half the sum of all its positive divisors: ( 1 + 2 + 3 + 6 ) / 2 = 6. The next perfect number is 28 = 1 + 2 + 4 + 7 + 14. This is followed by the perfect numbers 496 and 8128.
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13. Write a JavaScript function to compute the factors of a positive integer.
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14. Write a JavaScript function to convert an amount into coins.
Sample function : amountTocoins(46, [25, 10, 5, 2, 1])
Here 46 is the amount. and 25, 10, 5, 2, 1 are coins.
Output : 25, 10, 10, 1
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15. Write a JavaScript function to compute the value of bn where n is the exponent and b is the base. Accept b and n from the user and display the results.
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16. Write a JavaScript function to extract unique characters from a string.
Example string : "thequickbrownfoxjumpsoverthelazydog"
Expected Output : "thequickbrownfxjmpsvlazydg"
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17. Write a JavaScript function to get the number of occurrences of each letter in a specified string.
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18. Write a function for searching JavaScript arrays with binary searches.
Note : A binary search searches by splitting an array into smaller and smaller chunks until it finds the desired value.
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19. Write a JavaScript function that returns array elements larger than a number.
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20. Write a JavaScript function that generates a string ID (specified length) of random characters.
Sample character list : "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789"
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21. Write a JavaScript function to get all possible subsets with a fixed length (for example 2) combinations in an array.
Sample array : [1, 2, 3] and subset length is 2
Expected output : [[2, 1], [3, 1], [3, 2], [3, 2, 1]]
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22. Write a JavaScript function that accepts two arguments, a string and a letter and the function will count the number of occurrences of the specified letter within the string.
Sample arguments : 'w3resource.com', 'o'
Expected output : 2
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23. Write a JavaScript function to find the first not repeated character.
Sample arguments : 'abacddbec'
Expected output : 'e'
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24. Write a JavaScript function to apply the Bubble Sort algorithm.
Note : According to wikipedia "Bubble sort, sometimes referred to as sinking sort, is a simple sorting algorithm that works by repeatedly stepping through the list to be sorted, comparing each pair of adjacent items and swapping them if they are in the wrong order".
Sample array : [12, 345, 4, 546, 122, 84, 98, 64, 9, 1, 3223, 455, 23, 234, 213]
Expected output : [3223, 546, 455, 345, 234, 213, 122, 98, 84, 64, 23, 12, 9, 4, 1]
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25. Write a JavaScript function that accepts a list of country names as input and returns the longest country name as output.
Sample function : Longest_Country_Name(["Australia", "Germany", "United States of America"])
Expected output : "United States of America"
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26. Write a JavaScript function to find the longest substring in a given string without repeating characters.
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27. Write a JavaScript function that returns the longest palindrome in a given string.

Note: According to Wikipedia "In computer science, the longest palindromic substring or longest symmetric factor problem is the problem of finding a maximum-length contiguous substring of a given string that is also a palindrome. For example, the longest palindromic substring of "bananas" is "anana". The longest palindromic substring is not guaranteed to be unique; for example, in the string "abracadabra", there is no palindromic substring with length greater than three, but there are two palindromic substrings with length three, namely, "aca" and "ada".
In some applications it may be necessary to return all maximal palindromic substrings (that is, all substrings that are themselves palindromes and cannot be extended to larger palindromic substrings) rather than returning only one substring or returning the maximum length of a palindromic substring.
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28. Write a JavaScript program to pass a 'JavaScript function' as a parameter.
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29. Write a JavaScript function to get the function name.
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## JavaScript: Tips of the Day

```const user = { name: 'Owen', age: 21 };