Explanation of how mangling works: in terser: https://terser.org/docs/cli-usage#cli-mangling-property-names-mangle-props

so I actually did get some property mangling to work with terser. I don't know how safe it is so I have it disabled for now but I basically fed it some regexes of package names in our project together with these important options.

1. nameCache, this makes sure it mangles the name to the same thing across files,
2. parallel: false, this makes sure it doesn't process the name mangling in parallel, this is a webpack specific thing. Other runners like vite might do something different.
3. keep_quoted: true, which as the option suggests won't mangle a name that ever appears quoted.

I used the following snippet, the reserved words I pulled from the ClosureLinkerBackend. I included some examples of packages this project uses. Anyways, not sure where to go with this outside of telling you I think it's possible with no work on the scalajs side, which is exciting.

{
    sourceMap: true,
    nameCache: {},
    format: {
      comments: false,
    },
    mangle: {
      properties: {
        debug: false,
        keep_quoted: true,
        reserved: ['$classData', 'main', 'toString', 'constructor', 'length', 'call', 'apply', 'NaN', 'Infinity', 'undefined'],
        regex: /^(Lweb|Lslinky|slinky|render__L|query__L|\$m_|.*__f_|Ljava|cats\$)/,
      }
    },
  }

I tried this and got a nice size reduction. However (I think this is expected) it doesn't work with dynamic loading. I think it won't know what names to call on the other js files if they are mangled independently

@cquiroz if you are talking about js.dynamicImport it worked for me with webpack 5. This is bundler specific, because it's highly dependent on how the bundler processes files, and nameCache being the "big" feature that makes it work.

@cquiroz if you are talking about js.dynamicImport it worked for me with webpack 5. This is bundler specific, because it's highly dependent on how the bundler processes files, and nameCache being the "big" feature that makes it work.

It works but not ideal, still need a solution for mangle properties reserved and regex.

I've had a look at the terser options, and it seems we should be able to make it work with Scala.js:

Doc: https://terser.org/docs/api-reference#mangle-properties-options

• It supports closure style property renaming based on quoting (mangle.properties.keep_quoted: "strict")
• It supports rewriting an existing source map.
• It supports not renaming top-level definitions.
• It supports reserved identifiers (which we might need for global scope idents in modules).
• It supports reserved properties (which we might need to avoid name clashes with exports).
• It supports multiple files as input.

Unclear to me is how to best integrate. To integrate it externally (based on the linking report only), we need to expose quite a bit of the guts of the linker:

• optimizeBracketSelects = false
• trackAllGlobalRefs = true (and add to report)
• assemble all required exported properties (unclear whether these need to be all to avoid clashes, or only the ones for the corejslib).

On the flipside, we wouldn't have to do anything for sourcemaps.

Actually, multiple modules may also work with Closure Compiler, there is --chunk option for some time already (former is --module), more details are in this stackoverflow answer. Basic idea is to specify multiple output files (modules) along with their dependencies:

--js commonfunctions.js
--chunk common:1
--js page1functions.js
--js page1events.js
--chunk page1:2:common
--js page2function.js
--chunk page2:1:common

and Scala.js has knowledge about inter-module dependencies, right?

That's not the problem. We've known about that for a while.

The problem is mainly that GCC refuses to consider and preserve import statements to "the outside world" that is not under its control.

Is this one of the issues? google/closure-compiler#3707

All the details are already in #3893.

@sjrd I was thinking of this limitation even when module kind is CommonJS:

require(moduleSet.modules.size <= 1,
        "Cannot use multiple modules with the Closure Compiler")