, SteveRichter wrote

*snip*

 How does the end user customize their apps to give them what they need without the source code?  With javascript I can inject code into the browser on the client side to do these things.

in many cases developers would not want to allow end users to inject code!

that aside some of what you said is a matter of planning the app.

for example a data grid can be made to copy data and that will generally work for excel or word to paste in.

date / calendar : use the right control and it's done!

each of the two is simple to do in an app.