Fabric.js在从JSON加载画布后在Node服务器上创建图像

I've been racking my brain the last couple of days trying to figure this out. In the app I'm writing, a user can upload two images, one that overlays the other. After placing one image on top of the other, they click a button and the canvas is converted to JSON and sent to a node (express) server. The canvas is then recreated by loading the JSON data to the canvas, calling toDataURL with a multiplier of 2 and writing the data to a png file. I've been racking my brain the last couple of d