functions.js

function spread(fn, length) {
  switch (length) {
    case 0:
      return function() {
        return fn()
      }
    case 1:
      return function(a) {
        return fn(a[0])
      }
    case 2:
      return function(a) {
        return fn(a[0], a[1])
      }
    case 3:
      return function(a) {
        return fn(a[0], a[1], a[2])
      }
    case 4:
      return function(a) {
        return fn(a[0], a[1], a[2], a[3])
      }
    default:
      return function(a) {
        return fn.apply(null, a)
      }
  }
}

function apply(fn, c, a) {
  let aLength = a ? a.length : 0
  if (c == null) {
    switch (aLength) {
      case 0:
        return fn()
      case 1:
        return fn(a[0])
      case 2:
        return fn(a[0], a[1])
      case 3:
        return fn(a[0], a[1], a[2])
      case 4:
        return fn(a[0], a[1], a[2], a[3])
      default:
        return fn.apply(null, a)
    }
  } else {
    switch (aLength) {
      case 0:
        return fn.call(c)
      default:
        return fn.apply(c, a)
    }
  }
}

export {spread, apply}