The lastIndexOf() function in JS returns the index of the very last occurrence of the element, passed into it as an argument, in the array, if it exists. If it does not exist the function returns -1.For example −[3, 5, 3, 6, 6, 7, 4, 3, 2, 1].lastIndexOf(3) would return 7.We are required to write a JavaScript function that have the same utility as the existing lastIndexOf() function.And then we have to override the default lastIndexOf() function with the function we just created. We will simply iterate from the back until we find the element and return its index.If we ... Read More

Suppose, we have an array of objects like this −const arr = [    {"firstName":"John", "value": 89},    {"firstName":"Peter", "value": 151},    {"firstName":"Anna", "value": 200},    {"firstName":"Peter", "value": 22},    {"firstName":"Anna", "value": 60} ];We are required to write a JavaScript function that takes in one such array and combines the value property of all those objects that have similar value for the firstName property.Therefore, for the above array, the output should look like −const output = [    {"firstName":"John", "value": 89},    {"firstName":"Peter", "value": 173},    {"firstName":"Anna", "value": 260} ];For each object, we will recursively find their similar objects(Similar objects ... Read More

Suppose we have an array of literals like this −const arr = [4, 6, , 45, 3, 345, , 56, 6];We are required to write a JavaScript function that takes in one such array and remove all the undefined elements from the array in place. We are only required to remove the undefined and empty values and not all the falsy values.Use a for loop to iterate over the array and Array.prototype.splice() to remove undefined elements in place.ExampleFollowing is the code −const arr = [4, 6, , 45, 3, 345, , 56, 6] const eliminateUndefined = arr => {   ... Read More

Suppose, we have two arrays like these −const arr1 = ['d', 'a', 'b', 'c'] ; const arr2 = [{a:1}, {c:3}, {d:4}, {b:2}];We are required to write a JavaScript function that accepts these two arrays. The function should sort the second array according to the elements of the first array.We have to sort the keys of the second array according to the elements of the first array. This will produce the following output −const output = [{d:4}, {a:1}, {b:2}, {c:3}];ExampleFollowing is the code −const arr1 = ['d', 'a', 'b', 'c'] ; const arr2 = [{a:1}, {c:3}, {d:4}, {b:2}]; const sortArray = ... Read More

Suppose, we have two arrays like these −const arr1 = [1, 2, 3, 4, 5, 6]; const arr2 = [9, 8, 7, 5, 8, 3];We are required to write a JavaScript function that takes in two such arrays and returns an array of absolute difference between the corresponding elements of the array.Therefore, for these arrays, the output should look like −const output = [8, 6, 4, 1, 3, 3];We will use a for loop and keep pushing the absolute difference iteratively into a new array and finally return the array.ExampleFollowing is the code −const arr1 = [1, 2, 3, 4, ... Read More

We are required to write a JavaScript function that takes in a number, say n, and an array of two numbers that represents a range. The function should return an array of n random elements all lying between the range provided by the second argument.ExampleFollowing is the code −const num = 10; const range = [5, 15]; const randomBetween = (a, b) => {    return ((Math.random() * (b - a)) + a).toFixed(2); }; const randomBetweenRange = (num, range) => {    const res = [];    for(let i = 0; i < num; ){       const random ... Read More

Suppose we have a string with digits like this −const str = '11222233344444445666';We are required to write a JavaScript function that takes in this string and returns an object that represents the count of each number in the string.Therefore, for this string, the output should be −const output = {    "1": 2,    "2": 4,    "3": 3,    "4": 7,    "5": 1,    "6": 3 };ExampleFollowing is the code −const str = '11222233344444445666'; const mapString = str => {    const map = {};    for(let i = 0; i < str.length; i++){       map[str[i]] ... Read More

We are required to write a JavaScript function that takes in an array of numbers that may contain some duplicate numbers.Our function should return the sum of all the unique elements (elements that only appear once in the array) present in the array.For example −If the input array is −const arr = [2, 5, 5, 3, 2, 7, 4, 9, 9, 11];Then the output should be 25We will simply use a for loop, iterate the array and return the sum of unique elements.ExampleFollowing is the code −const arr = [2, 5, 5, 3, 2, 7, 4, 9, 9, 11]; const ... Read More

Suppose we have an array of objects like this −const arr = [{a: 2, b: 5, c: 6}, {a:3, b: 4, d:1}, {a: 1, d: 2}];Each object is bound to have unique keys in itself (for it to be a valid object), but two different objects can have the common keys (for the purpose of this question)We are required to write a JavaScript function that takes in one such array and returns an object with all the unique keys present in the array and their values cumulative sum as the valueTherefore, the resultant object should look like −const output = ... Read More

Suppose we have an object like this −const obj = {    key1: 56,    key2: 67,    key3: 23,    key4: 11,    key5: 88 };We are required to write a JavaScript function that takes in this object and returns a sorted array like this −const arr = [11, 23, 56, 67, 88];Here, we sorted the object values and placed them in an array.ExampleFollowing is the code −const obj = {    key1: 56,    key2: 67,    key3: 23,    key4: 11,    key5: 88 }; const sortObject = obj => {    const arr = Object.keys(obj).map(el => {       return obj[el];    });    arr.sort((a, b) => {       return a - b;    });      return arr; }; console.log(sortObject(obj));OutputThis will produce the following output in console −[ 11, 23, 56, 67, 88 ]