functional js trampoline

notreallyasolution.js

function repeat(operation, num) {
    if (num <= 0) {
        return num
    }
    else {
        operation()
        num--
        return num
    }
}

function trampoline(fn, op, num) {
    while ((num = fn(op, num) ) > 0) {
    }
}

module.exports = function (operation, num) {
    return trampoline(repeat, operation, num)
}

realsolution.js

  function repeat(operation, num) {
    if (num <= 0) return
    return function() {
      operation()
      return repeat(operation, --num)
    }
  }

  function trampoline(fn) {
    while(fn && typeof fn === 'function') {
      fn = fn()
    }
  }

  module.exports = function(operation, num) {
    trampoline(function() {
      return repeat(operation, num)
    })
  }

the catch is that the repeat function either returns undefined, or a new function that wraps a smaller number