Super simple JavaScript git diff hunk header config

.gitattributes

*.js diff="javascript"

.gitconfig

# In git config: .git/config, ~/.gitconfig, /etc/gitconfig

[diff "javascript"]
    xfuncname = "^\\s*(.*?\\bfunction\\b.*?\\(.*?\\))"

Cool tip !
But this doesn't work for functions like this (ES2015 syntax):

class Foo {
  constructor () {
    this.bar = "baz"
  }

  getBar () {
    return this.bar
  }
}