medium_chained_function_wo.js

function is(x) {
  return {
    plus: (plus) => {
      return is(x + plus)
    },
    minus: (minus) => {
      return is(x - minus)
    },
    equalToTen: () => {
      return (x === 10)
    }
  }
}

console.log(is(5).plus(5).equalToTen())           // true
console.log(is(5).plus(5).plus(1).equalToTen())   // false
console.log(is(10).equalToTen())                  // true
console.log(is(11).minus(1).equalToTen())         // true