I imagine this is not meant for UI Designers. The layout creation process feels impractical and the drag and drop with the side menu to add internal elements is a bit confusing.

Overall, its got some cool ideas. I like the export to Node.js feature. Anyway, it may be easier to pick one design pattern ( i.e. Drag and Drop or control by side menu)the mixture is kinda clunky.

The cross-hairs on the draggable elements is also kinda confusing as that is not conventionally what it means. I recommend the closed hand icon for that ( a quick Google search of "drag cursor") will get you on your way.

Overall not bad, but I can't see myself using it for prototyping.