TL;DR It'll raise the bar to someone copying the code and trying to pass it off as their own. It won't prevent a dedicated person from doing so. But the primary way to protect your work isn't technical, it's legal.
This library compiles your JavaScript code into V8 bytecode, which protect your source code...
Well, we don't know it's V8 bytecode, but it's "compiled" in some sense. All we know is that it creates a "code cache" via the built-in vm.Script.prototype.createCachedData API, which is officially just a cache used to speed up recompiling the code a second time, third time, etc. In theory, you're supposed to also provide the original source code as a string to the vm.Script constructor. But if you go digging into Node.js's vm.Script and V8 far enough it seems to be the actual code in some compiled form (whether actual V8 bytecode or not), and the code string you give it when running is ignored. (The ByteNode library provides a dummy string when running the code from the code cache, so clearly the actual code isn't [always?] needed.)
I'm wondering is there anyway to Decompile byteNode therefore it's not secure enough.
Naturally, otherwise it would be useless because Node.js wouldn't be able to run it. I didn't find a tool to do it that already exists, but since V8 is open source, it would presumably be possible to find the necessary information to write a decompiler for it that outputs valid JavaScript source code which someone could then try to understand.
Experimenting with it, local variable names appear to be lost, although function names don't. Comments appear to get lost (this may not be as obvious as it seems, given that Function.prototype.toString is required to either return the original source text or a synthetic version [details]).
So if you run the code through a minifier (particularly one that renames functions), then run it through ByteNode (or just do it with vm.Script yourself, ByteNode is a fairly thin wrapper), it will be feasible for someone to decompile it into something resembling source code, but that source code will be very hard to understand. This is very similar to shipping Java class files, which can be decompiled (there's even a standard tool to do it in the JDK, javap), except that the format Java class files are well-documented and don't change from one dot release to the next (though they can change from one major release to another; new releases always support the older format, though), whereas the format of this data is not documented (though it's an open source project) and is subject to change from one dot release to the next.
Certain changes, such as changing the copyright message, are probably fairly easy to make to said source code. More meaningful changes will be harder.
Note that the code cache appears to have a checksum or other similar integrity mechanism, since directly editing the .jsc file to swap one letter for another in a literal string makes the code cache fail to load. So someone tampering with it (for instance, to change a copyright notice) would either need to go the decompilation/recompilation route, or dive into the V8 source to find out how to correct the integrity check.
Fundamentally, the way to protect your work is to ensure that you've put all the relevant notices in the relevant places such that the fact copying it is a violation of copyright is clear, then pursue your legal recourse should you find out about someone passing it off as their own.
