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JavaScript array - Exercises, Practice, Solution

JavaScript array [44 exercises with solution]

[An editor is available at the bottom of the page to write and execute the scripts.]

1. Write a JavaScript function to check whether an `input` is an array or not. Go to the editor
Test Data :
console.log(is_array('w3resource'));
console.log(is_array([1, 2, 4, 0]));
false
true
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2. Write a JavaScript function to clone an array. Go to the editor
Test Data :
console.log(array_Clone([1, 2, 4, 0]));
console.log(array_Clone([1, 2, [4, 0]]));
[1, 2, 4, 0]
[1, 2, [4, 0]]
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3. Write a JavaScript function to get the first element of an array. Passing a parameter 'n' will return the first 'n' elements of the array. Go to the editor
Test Data :
console.log(first([7, 9, 0, -2]));
console.log(first([],3));
console.log(first([7, 9, 0, -2],3));
console.log(first([7, 9, 0, -2],6));
console.log(first([7, 9, 0, -2],-3));
Expected Output :
7
[]
[7, 9, 0]
[7, 9, 0, -2]
[]
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4. Write a JavaScript function to get the last element of an array. Passing a parameter 'n' will return the last 'n' elements of the array. Go to the editor
Test Data :
console.log(last([7, 9, 0, -2]));
console.log(last([7, 9, 0, -2],3));
console.log(last([7, 9, 0, -2],6));
Expected Output :
-2
[9, 0, -2]
[7, 9, 0, -2]
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5. Write a simple JavaScript program to join all elements of the following array into a string. Go to the editor
Sample array : myColor = ["Red", "Green", "White", "Black"];
Expected Output :
"Red,Green,White,Black"
"Red,Green,White,Black"
"Red+Green+White+Black"
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6. Write a JavaScript program which accept a number as input and insert dashes (-) between each two even numbers. For example if you accept 025468 the output should be 0-254-6-8. Go to the editor
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7. Write a JavaScript program to sort the items of an array. Go to the editor
Sample array : var arr1 = [ 3, 8, 7, 6, 5, -4, 3, 2, 1 ];
Sample Output : -4,-3,1,2,3,5,6,7,8
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8. Write a JavaScript program to find the most frequent item of an array. Go to the editor
Sample array : var arr1=[3, 'a', 'a', 'a', 2, 3, 'a', 3, 'a', 2, 4, 9, 3];
Sample Output : a ( 5 times )
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9. Write a JavaScript program which accept a string as input and swap the case of each character. For example if you input 'The Quick Brown Fox' the output should be 'tHE qUICK bROWN fOX'. Go to the editor
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10. Write a JavaScript program which prints the elements of the following array. Go to the editor
Note : Use nested for loops.
Sample array : var a = [[1, 2, 1, 24], [8, 11, 9, 4], [7, 0, 7, 27], [7, 4, 28, 14], [3, 10, 26, 7]];
Sample Output :
"row 0"
" 1"
" 2"
" 1"
" 24"
"row 1"
------
------
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11. Write a JavaScript program to find the sum of squares of a numeric vector. Go to the editor
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12. Write a JavaScript program to compute the sum and product of an array of integers. Go to the editor
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13. Write a JavaScript program to add items in an blank array and display the items. Go to the editor
Sample Screen :
add elements in an blank array
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14. Write a JavaScript program to remove duplicate items from an array (ignore case sensitivity). Go to the editor
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15. We have the following arrays : Go to the editor
color = ["Blue ", "Green", "Red", "Orange", "Violet", "Indigo", "Yellow "];
o = ["th","st","nd","rd"]
Write a JavaScript program to display the colors in the following way :
"1st choice is Blue ."
"2nd choice is Green."
"3rd choice is Red."
- - - - - - - - - - - - -
Note : Use ordinal numbers to tell their position.
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16. Write a JavaScript program to find the leap years in a given range of years. Go to the editor
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17. Write a JavaScript program to shuffle an array. Go to the editor
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18. Write a JavaScript program to perform a binary search. Go to the editor
Note : A binary search or half-interval search algorithm finds the position of a specified input value within an array sorted by key value.
Sample array :
var items = [1, 2, 3, 4, 5, 7, 8, 9];
Expected Output :
console.log(binary_Search(items, 1)); //0
console.log(binary_Search(items, 5)); //4
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19. There are two arrays with individual values, write a JavaScript program to compute the sum of each individual index value from the given arrays. Go to the editor
Sample array :
array1 = [1,0,2,3,4];
array2 = [3,5,6,7,8,13];
Expected Output :
[4, 5, 8, 10, 12, 13]
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20. Write a JavaScript program to find duplicate values in a JavaScript array. Go to the editor
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21. Write a JavaScript program to flatten a nested (any depth) array. If you pass shallow, the array will only be flattened a single level. Go to the editor
Sample Data :
console.log(flatten([1, [2], [3, [[4]]],[5,6]]));
[1, 2, 3, 4, 5, 6]
console.log(flatten([1, [2], [3, [[4]]],[5,6]], true));
[1, 2, 3, [[4]], 5, 6]
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22. Write a JavaScript program to compute the union of two arrays. Go to the editor
Sample Data :
console.log(union([1, 2, 3], [100, 2, 1, 10]));
[1, 2, 3, 10, 100]
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23. Write a JavaScript function to find the difference of two arrays. Go to the editor
Test Data :
console.log(difference([1, 2, 3], [100, 2, 1, 10]));
["3", "10", "100"]
console.log(difference([1, 2, 3, 4, 5], [1, [2], [3, [[4]]],[5,6]]));
["6"]
console.log(difference([1, 2, 3], [100, 2, 1, 10]));
["3", "10", "100"]
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24. Write a JavaScript function to remove. 'null', '0', '""', 'false', 'undefined' and 'NaN' values from an array. Go to the editor
Sample array : [NaN, 0, 15, false, -22, '',undefined, 47, null]
Expected result : [15, -22, 47]
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25. Write a JavaScript function to sort the following array of objects by title value. Go to the editor
Sample object :

var library = [ 
   { author: 'Bill Gates', title: 'The Road Ahead', libraryID: 1254},
   { author: 'Steve Jobs', title: 'Walter Isaacson', libraryID: 4264},
   { author: 'Suzanne Collins', title: 'Mockingjay: The Final Book of The Hunger Games', libraryID: 3245}
   ];

Expected result : 

[[object Object] {
  author: "Suzanne Collins",
  libraryID: 3245,
  title:"Mockingjay:The Final Book of The Hunger Games"
}, [object Object] {
  author: "Bill Gates",
  libraryID: 1254,
  title: "The Road Ahead"
}, [object Object] {
  author: "Steve Jobs",
  libraryID: 4264,
  title: "Walter Isaacson"
}]

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26. Write a JavaScript program to find a pair of elements (indices of the two numbers) from an given array whose sum equals a specific target number. Go to the editor

Input: numbers= [10,20,10,40,50,60,70], target=50
Output: 2, 3

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27. Write a JavaScript function to retrieve the value of a given property from all elements in an array. Go to the editor
Sample array : [NaN, 0, 15, false, -22, '',undefined, 47, null]
Expected result : [15, -22, 47]
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28. Write a JavaScript function to find the longest common starting substring in a set of strings. Go to the editor

Sample array : console.log(longest_common_starting_substring(['go', 'google']));
Expected result : "go"

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29. Write a JavaScript function to fill an array with values (numeric, string with one character) on supplied bounds. Go to the editor

Test Data :
console.log(num_string_range('a', "z", 2));
["a", "c", "e", "g", "i", "k", "m", "o", "q", "s", "u", "w", "y"]

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30. Write a JavaScript function to merge two arrays and removes all duplicates elements. Go to the editor

Test data :
var array1 = [1, 2, 3];
var array2 = [2, 30, 1];
console.log(merge_array(array1, array2));
[3, 2, 30, 1]

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31. Write a JavaScript function to remove a specific element from an array. Go to the editor

Test data :
console.log(remove_array_element([2, 5, 9, 6], 5));
[2, 9, 6]
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32. Write a JavaScript function to find an array contains a specific element. Go to the editor

Test data :
arr = [2, 5, 9, 6];
console.log(contains(arr, 5));
[True]
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33. Write a JavaScript script to empty an array keeping the original. Go to the editor

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34. Write a JavaScript function to get nth largest element from an unsorted array. Go to the editor

Test Data :
console.log(nthlargest([ 43, 56, 23, 89, 88, 90, 99, 652], 4));
89

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35. Write a JavaScript function to get a random item from an array. Go to the editor

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36. Write a JavaScript function to create a specified number of elements with pre-filled numeric value array. Go to the editor

Test Data :
console.log(array_filled(6, 0));
[0, 0, 0, 0, 0, 0]
console.log(array_filled(4, 11));
[11, 11, 11, 11]

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37. Write a JavaScript function to create a specified number of elements with pre-filled string value array. Go to the editor

Test Data :
console.log(array_filled(3, 'default value'));
["default value", "default value", "default value"]
console.log(array_filled(4, 'password'));
["password", "password", "password", "password"]
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38. Write a JavaScript function to move an array element from one position to another. Go to the editor

Test Data :
console.log(move([10, 20, 30, 40, 50], 0, 2));
[20, 30, 10, 40, 50]
console.log(move([10, 20, 30, 40, 50], -1, -2));
[10, 20, 30, 50, 40]
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39. Write a JavaScript function to filter false, null, 0 and blank values from an array. Go to the editor

Test Data :
console.log(filter_array_values([58, '', 'abcd', true, null, false, 0]));
[58, "abcd", true]
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40. Write a JavaScript function to generate an array of specified length, filled with integer numbers, increase by one from starting position. Go to the editor

Test Data :
console.log(array_range(1, 4));
[1, 2, 3, 4]
console.log(array_range(-6, 4));
[-6, -5, -4, -3]
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41. Write a JavaScript function to generate an array between two integers of 1 step length. Go to the editor

Test Data :
console.log(rangeBetwee(4, 7));
[4, 5, 6, 7]
console.log(rangeBetwee(-4, 7));
[-4, -3, -2, -1, 0, 1, 2, 3, 4, 5, 6, 7]
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42. Write a JavaScript function to find the unique elements from two arrays. Go to the editor

Test Data :
console.log(difference([1, 2, 3], [100, 2, 1, 10]));
["1", "2", "3", "10", "100"]
console.log(difference([1, 2, 3, 4, 5], [1, [2], [3, [[4]]],[5,6]]));
["1", "2", "3", "4", "5", "6"]
console.log(difference([1, 2, 3], [100, 2, 1, 10]));
["1", "2", "3", "10", "100"]
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43. Write a JavaScript function to create an array of arrays, ungrouping the elements in an array produced by zip. Go to the editor

Test Data :
unzip([['a', 1, true], ['b', 2, false]])
unzip([['a', 1, true], ['b', 2]])
Expected Output:
[["a","b"],[1,2],[true,false]]
[["a","b"],[1,2],[true]]
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44. Write a JavaScript function to create an object from an array, using the specified key and excluding it from each value. Go to the editor

Test Data :
indexOn([ { id: 10, name: 'apple' }, { id: 20, name: 'orange' } ], x => x.id)
Expected Output:
{"undefined":{"id":20,"name":"orange"}}
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More to Come !

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JavaScript: Tips of the Day

Memoized function

const add = () => {
  const cache = {};
  return num => {
    if (num in cache) {
      return 'From cache! ${cache[num]}';
    } else {
      const result = num + 10;
      cache[num] = result;
      return 'Calculated! ${result}';
    }
  };
};

const addFunction = add();
console.log(addFunction(10));
console.log(addFunction(10));
console.log(addFunction(5 * 2));

The add function is a memoized function. With memoization, we can cache the results of a function in order to speed up its execution. In this case, we create a cache object that stores the previously returned values.
If we call the addFunction function again with the same argument, it first checks whether it has already gotten that value in its cache. If that's the case, the caches value will be returned, which saves on execution time. Else, if it's not cached, it will calculate the value and store it afterwards.
We call the addFunction function three times with the same value: on the first invocation, the value of the function when num is equal to 10 isn't cached yet. The condition of the if-statement num in cache returns false, and the else block gets executed: Calculated! 20 gets logged, and the value of the result gets added to the cache object. cache now looks like { 10: 20 }.
The second time, the cache object contains the value that gets returned for 10. The condition of the if-statement num in cache returns true, and 'From cache! 20' gets logged.
The third time, we pass 5 * 2 to the function which gets evaluated to 10. The cache object contains the value that gets returned for 10. The condition of the if-statement num in cache returns true, and 'From cache! 20' gets logged.

Ref: https://bit.ly/3jFRBje