polymer-web-scanner.js

handleClick() {
    if (DWObject) {
      let image = this.shadowRoot.querySelector('#image');
      DWObject.SelectSource(function () {
          var onSuccess, onFailure;
          onSuccess = onFailure = function () {
              DWObject.CloseSource();
              image.src = DWObject.GetImageURL(DWObject.CurrentImageIndexInBuffer, 640, 480);
          };
          DWObject.OpenSource();
          DWObject.IfDisableSourceAfterAcquire = true;
          DWObject.AcquireImage(onSuccess, onFailure);
      }, function () {
          console.log('SelectSource failed!');
      });
    }