The script below, in the **area** function, why is necessary to include *this.***radius** in the return? The variable **radius** works without *this*.

```
function Circle (radius) {
this.radius = radius;
this.area = function () {
return Math.PI * this.radius * this.radius;
};
// define a perimeter method here
this.perimeter = function() {
return 2 * Math.PI * radius;
};
};
```