Mousetrap will only bind a key event to one function, this makes it so you can bind it to as many as you like.

MousetrapProxy.js

class MousetrapProxy {
  constructor () {
    this.events = {}
  }

  emit (key) {
    if (!this.events[key]) return
    this.events[key].forEach((cb) => cb())
  }

  bind (keys, cb) {
    const keysArray = typeof keys === 'string' ? [keys] : keys
    keysArray.forEach((key) => {
      if (!this.events[key]) {
        this.events[key] = []
        Mousetrap.bind(key, () => {
          this.emit(key)
        })
      }
      this.events[key].push(cb)
    })
  }
}

var ee = new MousetrapProxy();

ee.bind(['command+shift+k', 'up'], function (e) {
  console.log('meow')
})

ee.bind('command+shift+k', function (e) {
  console.log('ruff')
})

(function () {
  const events = {}
  const _old_mousetrap = Mousetrap.bind

  Mousetrap.bind = (keys, cb) => {
    const keysArray = typeof keys === 'string' ? [keys] : keys
    keysArray.forEach((key) => {
      if (!events[key]) {
         events[key] = []
         _old_mousetrap(key, () => {
           events[key].forEach((event) => {
             event()
           })
        })
      }
      events[key].push(cb)
    })
  }
})()

Mousetrap.bind(['command+shift+k', 'up'], function (e) {
    console.log('meow')
})

Mousetrap.bind('command+shift+k', function (e) {
    console.log('ruff')
})