Practical use cases for returning javascript from an XHR/Ajax request?

I've never really had to return javascript from an XHR request. In the times I've needed to apply behaviour to dynamically loaded content I could always do it within my script making the call.

Could someone provide actual real world cases just so I'm aware, of when you'd actually need to do this ( not for convenience ), or some reasons of why in some cases it's better to return js along with the other content instead of building that functionality in your callback?

The only scenario that's coming to my head is on a heavily customized site, if the site supports multiple languages for example and the functionality changes depending on the language, and ajax is used to pull in dynamic content and perhaps in some languages a certain behavior needs to happen while in others another needs to happen and it's more efficient r开发者_开发知识库eturning js in script blocks instead of dumping all that logic into a callback.

Sometimes it is more convenient to "prepare" the JavaScript code on the server side. You can use the server's programming or scripting language to generate the code and you can fill it with values from the database. This way most of the logic takes place on the server and not the client. But it is really a matter of taste. OK, that wasn't a real world case but maybe my opinion is helpful anyway.

We use XHR to request an entire web page that includes java script for menus etc. We then replace the current page with the new one that has been sent over XHR