I have a legacy application that uses jQuery 1.4.2 and I need to update the version to the latest stable build, so that it doesn't have the vulnerabilities of the old version.
The code base is pretty huge and it would be a PITA to check everything and to migrate deprecated code. I found this project https://github.com/jquery/jquery-migrate which seems to do the trick... I've included that library in my code (actually 2 libraries, to migrate to 1.12 and then 1.12 to 3.0) and it displays a lot of warnings related to deprecated methods.
My question is this... Can I use the jquery-migrate library to have backward compatibility with deprecated/deleted functions, or is it intended only for logging the deprecated functions and I should fix all of them? Can I use it as it is in production?
Yes you can, you just need to use the production version of the library:
https://github.com/jquery/jquery-migrate#development-vs-production-versions
It is intended to keep projects that are in the process of upgrade in production