GreatstCommonDevider.js

function GCD(a,b){
  let res;
  for(let i = 0; i< Math.max(a,b); i++){
    if(a % i === 0 && b % i === 0){
      res = i;
    }
  }
  return res
}

function GCD(a,b){
  while(true){
    if(a === 0) return b;
    if(b === 0) return a;
    if(a >= b){    	
      a = a % b;   
    }
    else{
    	b = b % a;   
    }
  } 
}

function GCD(a,b){
  if(a === 0) return b;
  if(b === 0) return a;
  
  while(a !== b){    
    if(a > b){    	
      a = a - b;      
    }
    else{
    	a = b - a; 
      b = a;
    }
  }
  return a;
}