Steps to reproduce:

1. Adding the following code for creating in CInput("checkbox") element in widget.view.php

    <?php
       $powerLabel    = new CLabel("Power On/Off", "powerLabel");
       $powerLabel->addStyle("margin-left: 10px;");
       $powerLabel->addStyle("margin-right: 3px;");
       $powerCheckbox = new CInput("checkbox", "powerCheckbox", "on");
       $powerCheckbox->setId("powerCheckbox");
       $powerDiv      = new CDiv([$powerLabel, $powerCheckbox]);
       $widgetView = new CWidgetView($data);
       $widgetView->addItem($powerDiv);
       $widgetView->show();
   

2. Adding the following handling check status of CInput("checkbox") in class.widget.js 

   class WidgetAirConditioner  extends CWidget {
       static powerCheckboxChanged() {
           const powerCheckbox = document.getElementById('powerCheckbox');
               if (powerCheckbox) {
                   if (powerCheckbox.checked) {
                       console.log('Checkbox is checked.');
                   } else {
                       console.log('Checkbox is unchecked.');
                   }
       }
   
       onInitialize() {
       }
       
       onResize() {
       }
   
       processUpdateResponse(response) {
           super.processUpdateResponse(response);
       }
       
       promiseReady() {
           return super.promiseReady();
       }
       
       setContents(response) {
           super.setContents(response);
   
           const powerCheckbox = document.getElementById("powerCheckbox");
           if (powerCheckbox) {
               powerCheckbox.addEventListener('change', WidgetHitachiAirConditioner.powerCheckboxChanged);
           }
       }
       
       onClearContents() {
       }
   }
   

Result:
Check status of powerCheckbox is checked after user presses powerCheckbox. But after few seconds,  Check status of powerCheckbox is not checked.
Expected:
Check status of powerCheckbox is checked after user presses powerCheckbox. And after few seconds,  Check status of powerCheckbox is still checked.