Does fabricJS support SVG viewBox element so that it will render only that on canvas? That way, zooming of the entire screen could be implemented easily.
No, FabricJS is Canvas-based and Canvas and SVG are two very different realms.
FabricJS can parse SVG paths and draw them onto a canvas, but thats it.
Specifically, the SVG elements that FabricJS can parse and draw to a canvas are: path, circle, polygon, polyline, ellipse, rect, line, and image.