This is a dead end in a sufficiently large and complicated app (think beyond facebook/gmail etc) especially if the app supported multiple versions of 3rd party

This is a dead end in a sufficiently large and complicated app (think beyond facebook/gmail etc) especially if the app supported multiple versions of 3rd party code such as charting libs. besides writing it yourself (cue contractors going this is the only viable route) reuse and dead code elimination are necessary foundations to the next level of web apps for productivity of dev and responsive runtimes.