How to change font size of paragraph from drop down select option using javascript

How to change font size of paragraph from drop down select option using javascript 

Solution 

1. function changefontsize(a) 
   { 
    document. getElementById('para').style. fontSize=a+"px";
   } 

   calling 
   onchange="changefontsize(this.value)"

2. $("paragraph id/class").html(); 
   var dropdown value =$("#dropdownid option:selected").val()