I am Unable to get output in this JS

i am trying to make a simple claculator using JS in which i take all input from user i am a biginner completly kinda help me. secondly i also need to do same thing in php so how can i do that if someone has idea how to take input from user in core php. P.S no html no css is needed

<script type="text/javascript">
    do{
    var value1=prompt("enter 1st number::"," ");
    var value2=prompt("enter 2st number::"," ");
    var op=prompt("Enter operator from(+,-,*,/,%age,average):");
    if (op=="+")
    {
        var result=ParseInt(value1)+ParseInt(value2);
        document.write("addition result is ="+result );
        document.write("<br/>");
    }
    else if(op=="-")
        
    {
        var result1=ParseInt(value1)-ParseInt(value2);
        document.write("substraction result is ="+result1 );
        document.write("<br/>");
    }
    else if (op=="*")
    
        
    {
        var result2=ParseInt(value1)*ParseInt(value2);
        document.write("multiplication  result is ="+result2 );
        document.write("<br/>");
    }
    else if (op=="/")
    
       
    {
        var result3=ParseInt(value1)/ParseInt(value2);
        document.write("division  result is ="+result3 );
        document.write("<br/>");
    }
    else if (op=="%age")
    
       
    {
        var result4=(ParseInt(value1)/ParseInt(value2))*100;
        document.write("division  result is ="+result4 );
        document.write("<br/>");
    }
    else if (op=="average")
    
       
    {
        var result5=(ParseInt(value1)+ParseInt(value2))/2;
        document.write("division  result is ="+result5 );
        document.write("<br/>");
    }
    else
    {
        document.write("Invalid input :" );
        document.write("<br/>"); 
    }
    var choice=prompt("Do you want to continue (Y/N)::"," ");
    }
    while(choice=="Y"||choice=="y");
    </script>