We need to make sure that the new operator is always used.

gistfile1.txt

function User(first, last){ 
  if ( !(this instanceof User) ) 
    return new User(first, last); 
   
  this.name = first + " " + last; 
} 
 
var name = "Resig"; 
var user = User("John", name); 
 
assert( user, "This was defined correctly, even if it was by mistake." ); 
assert( name == "Resig", "The right name was maintained." );

function User(first, last){
if ( !(this instanceof arguments.callee) )
return new User(first, last);

this.name = first + " " + last;
}