niklasvh/html2canvas ? reverse-engineered prompt

Build me a browser based screenshot tool that can turn any webpage or part of a page into a canvas image from the DOM, without needing a server render. I want to be able to pass in an element and get back a promise that resolves with a canvas, then I can append it to the page or save it as an image.

It should work in the browser, handle common styles and page content as well as possible, and include a simple demo page where I can try it on different elements. Please make sure it has a build setup, example usage, and tests so I can verify the rendering behavior. If you need to check current browser support details or docs online, feel free to do that.