word-count.js

const counter = () => ({
  count: s => {
    return 'haha' + s
  }
})

class counter {
  count(s) {
    return 'haha' + s
  }
}

function counter () {
  this.count = (s) => 'haha' + s
}

let cc = new counter()
console.log(cc.count('ha'))