Before you drag and drop the image,there was nothing in assetManager

@ionic666 you can read Asset API documentation here There is no image in your asset manager. It seems you haven't added it yet. You can add like this..

grapesjs.init({
....
.....
 assetManager: {
          assets: [
                  {
                  type: 'image',
                  src: 'http://via.placeholder.com/250x350/0174DF/ffffff/',
                  date: '2018-06-28',
                  height: 350,
                  width: 250
                    },
                  {
                  type: 'image',
                  src: 'http://via.placeholder.com/250x350/5FB404/ffffff/',
                  date: '2018-06-28',
                  height: 350,
                  width: 250
                    }
            ]
          }
....
....
})

@ronaldaug i have done it.but I mean that if i haven't drag the image component,I cannot set background images for other components. The official demo was also not available

Maybe, you didn't add the component type as image. Make sure you add it. And you can just double click on the image to trigger the assets images box.

Could you share your codes via codepen or jsfiddle?

Do you mean this official demo ? I can see the images under Flex is the new black section do not work. It's because the images were added via CSS codes.