JavaScript如何使用prototype给对象定义属性

下面的JS代码定义了movie对象。在使用对象的过程中又通过prototype给对象添加了isComedy属性，调用的时候直接使用object.isComedy即可，非常方便。

<script type="text/javascript"> <!--
function movieToString() {
   return("title: "+this.title+"  director: "+this.director);
   }
function movie(title, director) {
   this.title = title;
   this.director = director || "unknown"; //if null assign to "unknown"
   this.toString = movieToString; //assign function to this method pointer
   }
   
var officeSpace = new movie("OfficeSpace");
var narnia = new movie("Narnia","Andrew Adamson");
movie.prototype.isComedy = false; //add a field to the movie's prototype
document.write(narnia.toString());
document.write("<br />Narnia a comedy? "+narnia.isComedy);
officeSpace.isComedy = true; //override the default just for this object
document.write("<br />Office Space a comedy? "+officeSpace.isComedy);
//-->
</script>