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index.js ➔ isPrime   D
last analyzed

↳ Parent: index.js

Complexity

Conditions 13

Size

Total Lines 43
Code Lines 26

Duplication

Lines 0
Ratio 0 %

Importance

Changes 0
Metric Value
cc 13
eloc 26
dl 0
loc 43
rs 4.2
c 0
b 0
f 0

How to fix   Complexity   

Complexity

Complex classes like index.js ➔ isPrime often do a lot of different things. To break such a class down, we need to identify a cohesive component within that class. A common approach to find such a component is to look for fields/methods that share the same prefixes, or suffixes.

Once you have determined the fields that belong together, you can apply the Extract Class refactoring. If the component makes sense as a sub-class, Extract Subclass is also a candidate, and is often faster.

1 
/**
2 
 *
3 
 * @author Henrik Fredriksson
4 
 * @param {*} n Integer to be tested for primality
5 
 * @param {number} [k=100] iteratons
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6 
 * @returns {boolean} True if n is prime otherwise false
7 
 */
8 
function isPrime(n, k = 100) {
9 
  if (n === 2 || n === 3) { return true }
10 

            


            
                                                                        
                            
            
                                    
            
            

                
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  const smallPrimes = [2, 3, 5, 7, 11, 13, 17]

            


            
                                                                        
                            
            
                                    
            
            

                
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  const res = smallPrimes.map(x => n % x === 0).filter(x => x).includes(true)

            


            
                                                                        
                            
            
                                    
            
            

                
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  if (res) return false

            


                            

                    
                        
                    
                    
                    
                    
                                                                                                    
                        

                            
                            
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            Coding Style
            Best Practice
    
    
    
        introduced 
                            by 
            

        

        

            
        

        

            

                

                    
                
                
            


        

    

    

        
                        

                            
                                
                            
                        

                                        
Curly braces around statements make for more readable code and help prevent bugs when you add further statements.
                                            

                    
                                            

                            

                            

                                
                                    
                                
                            


                            
Consider adding curly braces around all statements when they are executed conditionally.
This is optional if there is only one statement, but leaving them out can lead to unexpected
behaviour if another statement is added later.


Consider:


if (a > 0)
    b = 42;





If you or someone else later decides to put another statement in, only the first
statement will be executed.


if (a > 0)
    console.log("a > 0");
    b = 42;





In this case the statement b = 42 will always be executed, while
the logging statement will be executed conditionally.


if (a > 0) {
    console.log("a > 0");
    b = 42;
}





ensures that the proper code will be executed conditionally no matter how
many statements are added or removed.


                        

                                                    

                     Loading history...
                

                    


    




                                                                                    


                    		
                

            
                                                                        
                            
            
                                    
            
            

                
                    15
                

                                    
                                                    
                
                
                

            


            
                                                                        
                            
            
                                    
            
            

                
                    16
                

                                    
                                                    
                
                
                
  if (

            


            
                                                                        
                            
            
                                    
            
            

                
                    17
                

                                    
                                                    
                
                
                
    n % 2 === 0 || n % 3 === 0 || n % 5 === 0 || n % 7 === 0 || n < 2) {

            


            
                                                                        
                            
            
                                    
            
            

                
                    18
                

                                    
                                                    
                
                
                
    return false

            


            
                                                                        
                            
            
                                    
            
            

                
                    19
                

                                    
                                                    
                
                
                
  }

            


            
                                                                        
                            
            
                                    
            
            

                
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                    21
                

                                    
                                                    
                
                
                
  // Write (n - 1) as 2^s * d

            


            
                                                                        
                            
            
                                    
            
            

                
                    22
                

                                    
                                                    
                
                
                
  let s = 0

            


            
                                                                        
                            
            
                                    
            
            

                
                    23
                

                                    
                                                    
                
                
                
  let d = n - 1

            


            
                                                                        
                            
            
                                    
            
            

                
                    24
                

                                    
                                                    
                
                
                
  while (d % 2 === 0) {

            


            
                                                                        
                            
            
                                    
            
            

                
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    d /= 2

            


            
                                                                        
                            
            
                                    
            
            

                
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    ++s

            


            
                                                                        
                            
            
                                    
            
            

                
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  }

            


            
                                                                        
                            
            
                                    
            
            

                
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  const witness = n => {

            


            
                                                                        
                            
            
                                    
            
            

                
                    30
                

                                    
                                                    
                
                
                
    return Math.floor(Math.random() * (n - 2)) + 2

            


            
                                                                        
                            
            
                                    
            
            

                
                    31
                

                                    
                                                    
                
                
                
  }

            


            
                                                                        
                            
            
                                    
            
            

                
                    32
                

                                    
                                                    
                
                
                

            


            
                                                                        
                            
            
                                    
            
            

                
                    33
                

                                    
                                                    
                
                
                
  while (k--) {

            


            
                                                                        
                            
            
                                    
            
            

                
                    34
                

                                    
                                                    
                
                
                
    let a = Math.pow(witness(n), s)

            


            
                                                                        
                            
            
                                    
            
            

                
                    35
                

                                    
                                                    
                
                
                

            


            
                                                                        
                            
            
                                    
            
            

                
                    36
                

                                    
                                                    
                
                
                
    if (a % n === 1) continue

            


                            

                    
                        
                    
                    
                    
                    
                                                                                                    
                        

                            
                            
0 ignored issues

                            –
                            show
                        


                        

                                                                                        




    

        
            Coding Style
            Best Practice
    
    
    
        introduced 
                            by 
            

        

        

            
        

        

            

                

                    
                
                
            


        

    

    

        
                        

                            
                                
                            
                        

                                        
Curly braces around statements make for more readable code and help prevent bugs when you add further statements.
                                            

                    
                                            

                            

                            

                                
                                    
                                
                            


                            
Consider adding curly braces around all statements when they are executed conditionally.
This is optional if there is only one statement, but leaving them out can lead to unexpected
behaviour if another statement is added later.


Consider:


if (a > 0)
    b = 42;





If you or someone else later decides to put another statement in, only the first
statement will be executed.


if (a > 0)
    console.log("a > 0");
    b = 42;





In this case the statement b = 42 will always be executed, while
the logging statement will be executed conditionally.


if (a > 0) {
    console.log("a > 0");
    b = 42;
}





ensures that the proper code will be executed conditionally no matter how
many statements are added or removed.


                        

                                                    

                     Loading history...
                

                    


    




                                                                                    


                    		
                

            
                                                                        
                            
            
                                    
            
            

                
                    37
                

                                    
                                                    
                
                
                

            


            
                                                                        
                            
            
                                    
            
            

                
                    38
                

                                    
                                                    
                
                
                
    let testFails = false

            


            
                                                                        
                            
            
                                    
            
            

                
                    39
                

                                    
                                                    
                
                
                
    for (let i = 0; i < s; i++) {

            


            
                                                                        
                            
            
                                    
            
            

                
                    40
                

                                    
                                                    
                
                
                
      a = Math.pow(a, 2) % n

            


            
                                                                        
                            
            
                                    
            
            

                
                    41
                

                                    
                                                    
                
                
                
      if (a === n - 1) {

            


            
                                                                        
                            
            
                                    
            
            

                
                    42
                

                                    
                                                    
                
                
                
        testFails = true

            


            
                                                                        
                            
            
                                    
            
            

                
                    43
                

                                    
                                                    
                
                
                
        break

            


            
                                                                        
                            
            
                                    
            
            

                
                    44
                

                                    
                                                    
                
                
                
      }

            


            
                                                                        
                            
            
                                    
            
            

                
                    45
                

                                    
                                                    
                
                
                
    }

            


            
                                                                        
                            
            
                                    
            
            

                
                    46
                

                                    
                                                    
                
                
                

            


            
                                                                        
                            
            
                                    
            
            

                
                    47
                

                                    
                                                    
                
                
                
    if (testFails) return false

            


                            

                    
                        
                    
                    
                    
                    
                                                                                                    
                        

                            
                            
0 ignored issues

                            –
                            show
                        


                        

                                                                                        




    

        
            Coding Style
            Best Practice
    
    
    
        introduced 
                            by 
            

        

        

            
        

        

            

                

                    
                
                
            


        

    

    

        
                        

                            
                                
                            
                        

                                        
Curly braces around statements make for more readable code and help prevent bugs when you add further statements.
                                            

                    
                                            

                            

                            

                                
                                    
                                
                            


                            
Consider adding curly braces around all statements when they are executed conditionally.
This is optional if there is only one statement, but leaving them out can lead to unexpected
behaviour if another statement is added later.


Consider:


if (a > 0)
    b = 42;





If you or someone else later decides to put another statement in, only the first
statement will be executed.


if (a > 0)
    console.log("a > 0");
    b = 42;





In this case the statement b = 42 will always be executed, while
the logging statement will be executed conditionally.


if (a > 0) {
    console.log("a > 0");
    b = 42;
}





ensures that the proper code will be executed conditionally no matter how
many statements are added or removed.


                        

                                                    

                     Loading history...
                

                    


    




                                                                                    


                    		
                

            
                                                                        
                            
            
                                    
            
            

                
                    48
                

                                    
                                                    
                
                
                
  }

            


            
                                                                        
                            
            
                                    
            
            

                
                    49
                

                                    
                                                    
                
                
                
  return true

            


            
                                                                        
                            
            
                                    
            
            

                
                    50
                

                                    
                                                    
                
                
                
}

            


            
                                                                                                            
                            
            
                                    
            
            

                
                    51
                

                                    
                                                    
                
                
                

            


            
                                                                                                            
                                                                
            
                                    
            
            

                
                    52
                

                                    
                                                    
                
                
                
module.exports = isPrime

            


            
                                                        
            
                                    
            
            

                
                    53