How to change the radius of the circle around the marker in Google Map API

I am trying to change the circle radius by changing the value of combo-menu. So I wrote the 开发者_开发问答a function for onchange as below.

    function changeRadius(){ 
       var selectedRadius = (document.getElementById("circle_radius").value)*1000;

       var circle = new google.maps.Circle({
              map: map,
              radius: selectedRadius // radius unit is meter.
            });

       var marker2 = new google.maps.Marker({
              map: map,
              position: new google.maps.LatLng(40,-90),
              draggable: true,
              title: 'Drag me!'
            });

       circle1.bindTo('center', marker2, 'position'); 

   }

But It doesn't work. Any idea?

You'll have to do something like this:

google.maps.event.addDomListener(
   document.getElementById('circle_radius'), 'change', function() {
       circle.setRadius(document.getElementById('circle_radius').value)
   });

with this function you'll set up a function as listener for the circle_radius combo value change event. The function will update the radius of your circle with the value of the combo.