Modernize internal JS code and run it through eslint. NFC

[sbc100]

This change does not effect the JS that we output, only the the internal
JS tooling.

One of the interesting changes here is the use of the global object
to share symbols between JS files. In the current setup each JS file
is read in using eval. The only way to share symbol between such
files is via the global namespace which means either a naked variable
declaration (with no const, let or var), or directly using the
global namespace. As a followup we can hopefully remove the use of
eval for the files that are part of this PR.

The long list of exclusions in .eslintrc.yml is because these files
are part of the JS library code which we ship and we a lot of that
cannot be run though the lint tool because it uses our speciall
pre-processing techniques.

This is a followup to #15838 and #15836 which did this for two
individual entry points.

[aheejin]

Given that my knowledge of JS is fairly limited, I might ask some basic questions.

One of the interesting changes here is the use of the global object to share symbols between JS files.

Where is this global object defined? Is that our custom object? Can we use globalThis instead?

The only way to share symbol between such files is via the global namespace which means either a naked variable declaration (with no const, let or var),

var variables seem to be global when they are declared outside a function though?

a lot of that cannot be run though the lint tool because it uses our speciall pre-processing techniques.

Do you mean minifying? If so, is there a reason we can't minify linted JS?

[sbc100]

Given that my knowledge of JS is fairly limited, I might ask some basic questions.

One of the interesting changes here is the use of the global object to share symbols between JS files.

Where is this global object defined? Is that our custom object? Can we use globalThis instead?

global is defined by node itself: https://nodejs.org/api/globals.html#globals_global.

From looking at the docs it looks like globalThis and global are the same thing under nodejs, which means we could use either. I don't think I know enough about node to say which would be better in this particular case... but at least using global will leave the reader knowing for sure that this is a script that is only designed be run under node (we do not support the running of these scripts on the web for example).

The only way to share symbol between such files is via the global namespace which means either a naked variable declaration (with no const, let or var),

var variables seem to be global when they are declared outside a function though?

We may be able to use var instead of assignments to global (or globalThis) but in this change we are moving completely away from the use of var and instead using only the new const and let. They use of var is prohibited by eslint. In addition, I think the use of the global object here make clear the intent to share with other scripts.

a lot of that cannot be run though the lint tool because it uses our speciall pre-processing techniques.

Do you mean minifying? If so, is there a reason we can't minify linted JS?

emscripten's JS library uses a special pre-processor that implements #if and #else and #endif as well as inline {{{ macros }}}. eslint cannot understand this syntax at all sadly.

[aheejin]

Thanks for the explanation!