Instances of '#key#' within a JS file are resolved on the server-side for a language (en_US, for example) when the file is first requested from a client. Subsequent requests are fast because the internationalized version of the file is already generated. Note that this only happens for JS files under the web/public/jsmodules/ folder.

I would recommend using '#key#' whenever possible because it will be faster to execute on the client. You should use Labels.get('key') when:

• You have to construct the key at runtime
• The message label includes arguments (ex: message.key=Failed with error: {0})
• You are working in a JS file that is included within build.jsb; in other words, it does not live under web/public/jsmodules/