code: function initRadio(elem, parsed){
    var self = this;
    var wc = this.$watch(parsed, function( newValue ){
      if(newValue == elem.value) elem.checked = true;
      else elem.checked = false;
    }, STABLE);
  
  
    var handler = function handler(){
      var value = this.value;
      parsed.set(self, value);
      self.$update();
    }
    if(parsed.set) dom.on(elem, "change", handler)
    // beacuse only after compile(init), the dom structrue is exsit. 
    if(parsed.get(self) === undefined){
      if(elem.checked) {
        parsed.set(self, elem.value);
      }
    }
  
    return function destroy(){
      if(parsed.set) dom.off(elem, "change", handler)
    }
  }
docs: input:radio binding