Prime Number Check in JavaScript

1// Prime number: divisible only by 1 and itself
2// Examples: 2, 3, 5, 7, 11, 13, 17, 19
3
4// Method 1: Basic check
5function isPrime(n) {
6    if (n < 2) return false;
7    if (n === 2) return true;
8    if (n % 2 === 0) return false;
9    
10    for (let i = 3; i < n; i += 2) {
11        if (n % i === 0) return false;
12    }
13    return true;
14}
15
16console.log("2:", isPrime(2));
17console.log("4:", isPrime(4));
18console.log("17:", isPrime(17));
19console.log("20:", isPrime(20));
20
21// Method 2: Optimized (check up to sqrt(n))
22function isPrimeOptimized(n) {
23    if (n < 2) return false;
24    if (n === 2) return true;
25    if (n % 2 === 0) return false;
26    
27    let sqrt = Math.sqrt(n);
28    for (let i = 3; i <= sqrt; i += 2) {
29        if (n % i === 0) return false;
30    }
31    return true;
32}
33
34console.log("\nOptimized:");
35console.log("29:", isPrimeOptimized(29));
36console.log("100:", isPrimeOptimized(100));
37
38// Method 3: Find primes in range
39function findPrimesInRange(start, end) {
40    let primes = [];
41    for (let i = start; i <= end; i++) {
42        if (isPrimeOptimized(i)) {
43            primes.push(i);
44        }
45    }
46    return primes;
47}
48
49console.log("\nPrimes between 10 and 30:");
50console.log(findPrimesInRange(10, 30));
51
52// Method 4: Count prime factors
53function countPrimeFactors(n) {
54    let count = 0;
55    let factors = [];
56    
57    for (let i = 2; i <= n; i++) {
58        while (n % i === 0) {
59            count++;
60            factors.push(i);
61            n /= i;
62        }
63    }
64    
65    return { count, factors };
66}
67
68console.log("\nPrime factors of 60:");
69console.log(countPrimeFactors(60));