Here is an idea that is not as simple as just directly implementing js as jsp, but is probably more performant and maintainable: for each js, we also have a corresponding jsp. For example

Foo.js
Foo.js.jsp

Within Foo.js, it's pure static javascript, but optionally with "hook"'s that the Foo.js.jsp can fill in during runtime on the enclosing page. For example:

Foo.js
------
// Constructor of the Javascript Foo class.
function Foo() {}
...
// Anytime it needs to access a dynamic property that needs 
// to be determined by the Java App, or tag lib, or whatever, 
// use a class level variable.
// For example, a i18n message to be displayed.
alert(Foo.FOO_MESSAGE);
...

Foo.js.jsp
----------
// Foo.js.jsp is included in the main page where the reference to Foo.js is made.
// If there is no dynamic content, Foo.js.jsp just evaluates to do nothing.
Foo.FOO_MESSAGE = "<c:out name="${fooMessage}" />"

This way, all the dynamic content are included as Javascript class level variables in the main page, and the static Foo.js just refers to these variables.

Now all the *.js can be pushed to the Web server front end (eg Apache) - solves the performance issue. All the dynamic content is maintained in one single place: the respective jsp connected via a javascript class - solves the maintenance nightmare issue.