[Forge36]

Couple of weird language edge cases

JS allows functions to by called by name.

A.foo();

Can be

A["foo"]()

Because foo is now a string it's possible to add levels of indirection.

Action(name) { A[name](); }

It's possible the list of actions to perform are sent to the client as data.

This amiguity has left enough doubt for most tools, and people making tree shaking a practice on code not commonly performed. The longer that happens the scarier it becomes to start investigating.

Since the browser will tree shake for you the incentive to cleanup your source is also less important.

[chadlavi]

But in this case A is exported. No one is going to tree shake methods of a class.

[arp242]

It doesn't need to be a class; that's a detail:

  function foo() { ... }
  var callthis = "foo"
  window[callthis]()

And this is true for any object; attaching functions to objects is kinda common.

And of course, "callthis" is usually defined in a much more complex way, such as if (user_input_is_this) callthis = "foo" else callthis = "bar". Or what about callthis = "foo"; callthis += "_bar"?

In general this kind of stuff is tricky in dynamic languages (and also in static languages once you start using reflection); JavaScript isn't really an exception here. You really need to have a deep understanding of the code and logic to truly be certain that something will never be called.

[zelphirkalt]

> [...] Often contrasted with traditional single-library dead code elimination techniques common to minifiers, tree shaking eliminates unused functions from across the bundle by starting at the entry point and only including functions that may be executed.

Assuming, that methods of classes count as "function" in the terminology of that wiki page, then it seems to say methods of a class are shaken out. If they are not seen as functions (again, in that terminology), then I guess not.

[kroltan]

I think the article is over-simplifying, I believe most tree-shaking is done at the `import`/`export` boundaries.

Code that isn't used locally in a module and is not imported by any other modules is omitted.

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It helps that there isn't a global object for the local module scope, otherwise in-module dead code detection would also not be possible, since any line of code within it could use dynamic access and static analysis wouldn't be able to prove that it isn't used.