Question

How to check if a number is prime in JavaScript

Answer 1

function isPrime(n) {
    if (n == 0) return 0;
    if (n == 1) return 0;
    
    for (var i = 2; i <= Math.sqrt(n); i++) {
        if (n % i == 0) {
            return 0;
        }
    }
    
    return 1;
}
 
for (let i = 0; i < 20; i++) {
    let n = parseInt(Math.random() * 100);
    if (isPrime(n)) {
        console.log(n + " - Prime");
    }
    else {
        console.log(n + " - Not Prime");
    }
}

  
     
/*
run:
          
12 - Not Prime
37 - Prime
14 - Not Prime
39 - Not Prime
90 - Not Prime
5 - Prime
91 - Not Prime
81 - Not Prime
84 - Not Prime
66 - Not Prime
54 - Not Prime
35 - Not Prime
61 - Prime
69 - Not Prime
47 - Prime
45 - Not Prime
56 - Not Prime
72 - Not Prime
59 - Prime
72 - Not Prime
             
*/

 

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Answer 2

function isPrime(n) {
    if (n < 2 || (n % 2 == 0 && n != 2)) {
        return 0;
    }
  
    const count = Math.floor(Math.sqrt(n));
    
    for (let i = 3; i <= count; i += 2) {
        if (n % i == 0) {
            return 0;
        }
    }
    
    return 1;
}
  
const n = 97;
  
if (isPrime(n)) {
    console.log("Prime number");
} else {
    console.log("Not prime number");
}

  
  
  
/*
run:
  
Prime number
  
*/

 

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