Prime Numbers using JavaScript

HTML

<div id="output"></div>

JavaScript

function isPrime(number){     
      d = number-1;
      // If n is less than 2 or not an integer then we can say not a prime number.
   	if (number < 2) {
   			alert('If n is less than 2 or not an integer then we can say not a prime number.');
        return false
    }
   	if (number != Math.round(number)) {
    	  alert('If n is less than 2 or not an integer then we can say not a prime number.');
   		  return false
    }
   
    while (d > 1){
        if ((number % d) == 0)   
        {
           return false;
        }
        d--;
      }
      return true;       
    }
    
    if (isPrime(1)){
      alert('Prime number');
    }
    else{
      alert('Not Prime number');
    }
    

var val = isPrime(1);
document.getElementById('output').innerHTML = val;