What are Node.js "Linked" modules?

[thefourtheye]

When I was going through the source code, I found this in node.cc,

// "Linked" modules are included as part of the node project.
// Like builtins they are registered *before* node::Init runs.
mp->nm_flags = NM_F_LINKED;

Does anybody know what "Linked" modules are? @bnoordhuis maybe?

---

cc @addaleax

[mscdex]

It's probably this in the build script:

parser.add_option("--link-module",
    action="append",
    dest="linked_module",
    help="Path to a JS file to be bundled in the binary as a builtin."
         "This module will be referenced by path without extension."
         "e.g. /root/x/y.js will be referenced via require('root/x/y')."
         "Can be used multiple times")

[addaleax]

@mscdex That’s something different. The linked modules the C++ source is talking about would be native modules that are compiled into (or LD_PRELOLADed into?) the node executable itself, not JS code.

[mscdex]

Well, that's not confusing ;-)

[bnoordhuis]

The configure switch is for baking third-party JS source code into the binary, NM_F_LINKED is for bundling add-ons into the binary. Unfortunate name clash, yes.

[addaleax]

@bnoordhuis Is there anybody who uses that feature? Would documenting it be a good idea?

[bnoordhuis]

I assume so, at least at the time, otherwise why bother making a pull request? Both features where requested and implemented by non-collaborators.

Documenting it: no reason not to, I suppose.

[snggeng]

Hi I'd like to work on this. This is my first time working on open source and I was wondering which part of the documentation this should go into, and generally the relevant parts of the source I should be looking at.

[gibfahn]

I guess it should go somewhere in https://nodejs.org/api/modules.html (source here)?

As mentioned above, for the Native module you probably want to start here:

node/src/node.cc

Lines 2595 to 2599 in 4359a93

	// "Linked" modules are included as part of the node project.
	// Like builtins they are registered *before* node::Init runs.
	mp->nm_flags = NM_F_LINKED;
	mp->nm_link = modlist_linked;
	modlist_linked = mp;

For the js module you probably want to start here:

node/configure

Lines 152 to 158 in 201ecef

	parser.add_option("--link-module",
	action="append",
	dest="linked_module",
	help="Path to a JS file to be bundled in the binary as a builtin."
	"This module will be referenced by path without extension."
	"e.g. /root/x/y.js will be referenced via require('root/x/y')."
	"Can be used multiple times")

@bnoordhuis are the two features functionally identical, except for the fact that one is for native addons and one is for js addons?

[snggeng]

Awesome, thanks for the tips @gibfahn I'll look into it.

[joyeecheung]

Reopen since the OP is asking about native modules and they are still not documented. Should be fixed by #19112

[apapirovski]

Sounds like this was addressed by @joyeecheung above. Closing.