Let’s say, we are required to write a JavaScript function that takes in a number, say n, and returns an array containing all the prime numbers upto n.For example − If the number n is 24, then the output should be −const output = [2, 3, 5, 7, 11, 13, 17, 19, 23];ExampleFollowing is the code −const num = 24; const isPrime = num => {    let count = 2;    while(count < (num / 2)+1){       if(num % count !== 0){          count++;          continue;       };       return false;    };    return true; }; const primeUpto = num => {    if(num < 2){       return [];    };    const res = [2];    for(let i = 3; i

Let’s say, we have an array of arrays of boolean like this −const arr = [[true, false, false], [false, false, false], [false, false, true]];We are required to write a function that merges this array of arrays into a one-dimensional array by combining the corresponding elements of each subarray using the AND (&&) operator.Let’s write the code for this function. We will be using Array.prototype.reduce() function to achieve this.ExampleFollowing is the code −const arr = [[true, false, false], [false, false, false], [false, false, true]]; const andMerge = (arr = []) => {    return arr.reduce((acc, val) => {       ... Read More

We have two arrays of numbers like these −const arr1 = [12, 54, 2, 4, 6, 34, 3]; const arr2 = [54, 2, 5, 12, 4, 1, 3, 34];We are required to write a JavaScript function that takes in two such arrays and returns the element from arrays that are not common to both.ExampleFollowing is the code −const arr1 = [12, 54, 2, 4, 6, 34, 3]; const arr2 = [54, 2, 5, 12, 4, 1, 3, 34]; const difference = (first, second) => {    const res = [];    for(let i = 0; i < first.length; i++){   ... Read More

We are required to write a function that counts how many of the elements are in the array below / above a given number.Following is our array of Numbers −const array = [54, 54, 65, 73, 43, 78, 54, 54, 76, 3, 23, 78];For example, if the number is 60, the answer should be five elements below it −54, 54, 43, 3, 23and five element par it −65, 73, 78, 76, 78ExampleFollowing is the code −const array = [54, 54, 65, 73, 43, 78, 54, 54, 76, 3, 23, 78]; const belowParNumbers = (arr, num) => {    return arr.reduce((acc, ... Read More

We are required to write an array function midElement() that returns the middlemost element of the array without accessing its length property and without using any kind of built-in loops.If the array contains an odd number of elements, we return the one, middlemost element, or if the array contains an even number of elements, we return an array of two middlemost elements.ExampleFollowing is the code −const arr = [14, 32, 36, 42, 45, 66, 87]; const array = [13, 92, 83, 74, 55, 46, 74, 82]; const midElement = (arr, ind = 0) => {    if(arr[ind]){       ... Read More

Let’s say, we are required to write a JavaScript function that takes in an array of numbers with duplicate entries and sums all the duplicate entries to one index.For example −If the input array is −const input = [1, 3, 1, 3, 5, 7, 5, 4];Then the output should be −const output = [2, 6, 7, 10, 4];That means all the duplicate ones are summed to index 0 and all the duplicate threes are summed to index 1 and so on.ExampleFollowing is the code −const input = [1, 3, 1, 3, 5, 7, 5, 4]; const mergeDuplicates = arr => ... Read More

Let’s say, we are required to write a function that takes in an array arr of string / number literals as the first argument and a number n as second argument.We are required to return an array of n subarrays, each of which contains at most arr.length / n elements. And the distribution of elements should be like this −The first element goes in the first subarray, second in second, third in third and so on.Once we have one element in each subarray, we again start with filling the first subarray with its second element.Similarly, when all subarrays have two ... Read More

We have two arrays of Numbers, and we are required to write a function, let’s say intersection() that computes their intersection and returns an array that contains the intersecting elements in any order. Each element in the result should appear as many times as it shows in both arrays.For example −If input is −arr1 = ['hello', 'world', 'how', 'are', 'you']; arr2 = ['hey', 'world', 'can', 'you', 'rotate'];Then the output should be −Output: ['world', 'you'];ApproachHad the arrays been sorted, we could have used the two pointer approach with initially both pointing to 0 the start of the respective array and we ... Read More

Let’s say, we have an array of numbers like this −const arr = [-1, -2, -1, 0, -1, -2, -1, -2, -1, 0, 1, 0];We are required to write a JavaScript function that counts the consecutive groups of non-negative (positives and 0) numbers in the array.Like here we have consecutive non-negatives from index 3 to 3 (only one element, but still a cluster) which forms one group and then from 9 to end of array forms the second group.Therefore, for this array, the function should return 2.ExampleFollowing is the code −const arr = [-1, -2, -1, 0, -1, -2, -1, ... Read More

Let’s say, we are required to write a JavaScript function that takes in an array of Numbers and returns a new array with elements as sum of two consecutive elements from the original array.For example, if the input array is −const arr = [3, 6, 3, 87, 3, 23, 2, 2, 6, 8];Then the output should be −const output = [9, 90, 26, 4, 14];ExampleFollowing is the code −const arr = [3, 6, 3, 87, 3, 23, 2, 2, 6, 8]; const twiceSum = arr => {    const res = [];    for(let i = 0; i < arr.length; i += 2){       res.push(arr[i] + (arr[i+1] || 0));    };    return res; }; console.log(twiceSum(arr));OutputThis will produce the following output in console −[ 9, 90, 26, 4, 14 ]