Map, Reduce, and Filter - JS Array Functions Explained with Code

const arr = [1, 2, 3, 4, 5];// pass a function to mapconst double = arr.map(x => x * 2);console.log(double);// expected output: Array [2, 4, 6, 8, 10]

const arr = [1, 2, 3, 4, 5];// Transformation logic:function binary(x) {    return x.toString(2);}const binaryArr1 = arr.map(binary);console.log(binaryArr1) //[ '1', '10', '11', '100', '101' ]// The above code can be rewritten as :const binaryArr2 = arr.map(function binary(x) {    return x.toString(2);//[ '1', '10', '11', '100', '101' ]})console.log(binaryArr2)// OR -> Arrow functionconst binaryArr3 = arr.map((x) => x.toString(2));console.log(binaryArr3)//[ '1', '10', '11', '100', '101' ]

const users = [    { firstName: "Neeraj", lastName: "Kumar", age: 25 },    { firstName: "Sandeep", lastName: "Kumar", age: 26 },    { firstName: "Mayank", lastName: "Roy", age: 25 },    { firstName: "Peter", lastName: "Mukherjee", age: 28 },];// Get array of full name : ["Neeraj Kumar", "Sandeep Kumar", ...]const fullNameArr = users.map((user) => user.firstName + " " + user.lastName);console.log(fullNameArr); // ["Neeraj Kumar", "Sandeep Kumar", ...]----------------------------------------------------------// Get the count/report of how many unique people with unique age are there// like: {25 : 2, 26 : 1, 28 : 1}const report = users.reduce((acc, curr) => {    if(acc[curr.age]) {        acc[curr.age] = ++ acc[curr.age] ;    } else {        acc[curr.age] = 1;    }    return acc;  //to every time return update object}, {})console.log(report) // {25 : 2, 26 : 1, 28 : 1}

const array = [5, 1, 3, 2, 6];// filter odd valuesfunction isOdd(x) {  return x % 2;}const oddArr = array.filter(isOdd); // [5,1,3]// Other way of writing the above:const oddArr = arr.filter((x) => x % 2);

const array = [5, 1, 3, 2, 6];// Calculate sum of elements of array - Non functional programming wayfunction findSum(arr) {  let sum = 0;  for (let i = 0; i < arr.length; i++) {    sum = sum + arr[i];  }  return sum;}console.log(findSum(array)); // 17// reduce function wayconst sumOfElem = arr.reduce(function (accumulator, current) {  accumulator = accumulator + current;  return accumulator;}, 0); console.log(sumOfElem); // 17

// find max inside array: Non functional programming way:const array = [5, 1, 3, 2, 6];function findMax(arr) {    let max = 0;    for(let i = 0; i < arr.length; i++ {        if (arr[i] > max) {            max = arr[i]        }    }    return max;}console.log(findMax(array)); // 6// using reduceconst output = arr.reduce((acc, current) => {    if (current > acc ) {        acc = current;    }    return acc;}, 0);console.log(output); // 6// acc is just a label which represent the accumulated value till now,// so we can also label it as max in this caseconst output = arr.reduce((max, current) => {    if (current > max) {        max= current;    }    return max;}, 0);console.log(output); // 6

// First name of all people whose age is less than 30const users = [    { firstName: "Neeraj", lastName: "Kumar", age: 25 },    { firstName: "Sandeep", lastName: "Kumar", age: 26 },    { firstName: "Mayank", lastName: "Roy", age: 25 },    { firstName: "Peter", lastName: "Mukherjee", age: 28 },];// function chainingconst output = users  .filter((user) => user.age < 30)  .map((user) => user.firstName);console.log(output); // Homework challenge: Implement the same logic using reduceconst output = users.reduce((acc, curr) => {  if (curr.age < 30) {    acc.push(curr.firstName);  }  return acc;}, []);console.log(output);