Stefano writes: "marc_record.js is a LGPL set of classes and methods for manipulating one MARC binary record: add/get/delete tags, display in HTML/XML format, etc. It can be used in web-browser applications. It is the basis of MEL -MARC Editor Lite [1]- (sorry, in Italian only). Please, let me know if there are other JavaScript libraries with these functionalities."
Links:
[1] http://www.pusc.it/bib/mel/index.html