Arrow function name doesn't have same highlight as regular function name about vim-javascript HOT 1 CLOSED

They are technically two different things. The first one is a function declaration -- the name sum in this case has special properties -- you can put that function declaration anywhere in the file (even as the last written code) but still use it anywhere (even on the first line of the file)

The second example is a function expression -- sumOne is not usable until AFTER sumOne is declared. This is also similar to how any other const or let works.

Anything after a const or a let -- is impossible for us to know what it is.

Take this crazy contrived example:

const sumOne = (() => {
  if (someValue) {
    return () => {};
  }
  return 2;
})()

sumOne could be either the number 2 or a function, which could be determined at runtime.

In other words, it's pretty out of scope for use to do any sort of highlighting that would require a language server to parse the file and figure out types for us.

from vim-javascript.