Looks cool, somebody should make a package that puts a nice API around it. However seems that those APIs are only in Chrome now, not Firefox or Safari.
For most cases, the Element Capture or Region Capture API should be sufficient: https://developer.mozilla.org/en-US/docs/Web/API/Screen_Capt...
Demos: https://mdn.github.io/dom-examples/screen-capture-api/elemen... https://mdn.github.io/dom-examples/screen-capture-api/region...
If you need cross-browser compatibility (and can't just use a canvas) then yeah html2canvas is the way to go