Array Methods: Filter, Map, Reduce in JavaScript

1let numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
2
3// FILTER: Creates new array with elements that pass test
4let evenNumbers = numbers.filter(num => num % 2 === 0);
5console.log("Original:", numbers);
6console.log("Even numbers (filter):", evenNumbers);
7
8let greaterThan5 = numbers.filter(num => num > 5);
9console.log("Numbers > 5:", greaterThan5);
10
11// MAP: Creates new array by transforming each element
12let doubled = numbers.map(num => num * 2);
13console.log("\nDoubled (map):", doubled);
14
15let squared = numbers.map(num => num ** 2);
16console.log("Squared:", squared);
17
18// REDUCE: Reduces array to single value
19let sum = numbers.reduce((acc, num) => acc + num, 0);
20console.log("\nSum (reduce):", sum);
21
22let product = numbers.reduce((acc, num) => acc * num, 1);
23console.log("Product:", product);
24
25// CHAINING: Combine multiple methods
26let result = numbers
27    .filter(num => num % 2 === 0)  // [2, 4, 6, 8, 10]
28    .map(num => num * 2)            // [4, 8, 12, 16, 20]
29    .reduce((acc, num) => acc + num, 0); // 60
30
31console.log("\nChained (even * 2, then sum):", result);
32
33// Real-world example: Processing user data
34let users = [
35    { name: "John", age: 25, active: true },
36    { name: "Jane", age: 30, active: false },
37    { name: "Bob", age: 20, active: true },
38    { name: "Alice", age: 35, active: true }
39];
40
41// Get names of active users over 25
42let activeOver25 = users
43    .filter(user => user.active && user.age > 25)
44    .map(user => user.name);
45
46console.log("\nActive users over 25:", activeOver25);
47
48// Calculate average age of active users
49let avgAge = users
50    .filter(user => user.active)
51    .map(user => user.age)
52    .reduce((acc, age, index, array) => {
53        acc += age;
54        if (index === array.length - 1) {
55            return acc / array.length;
56        }
57        return acc;
58    }, 0);
59
60console.log("Average age of active users:", avgAge);