update spec and polyfill code

Author: keithamus

README.md

@@ -34,8 +34,8 @@ When the GetLastArrayItem method is called, the following steps are taken:
  If len is zero, then
  Return undefined.
  Else len > 0,
- Let newLen be len-1.
- Let index be ! ToString(newLen).
+ Set len to len-1.
+ Let index be ! ToString(len).
  Let element be ? Get(O, index).
  Return element. 
 
@@ -48,7 +48,7 @@ When the SetLastArrayItem method is called, the following steps are taken:
  Let O be ? ToObject(this value).
  Let len be ? ToLength(? Get(O, "length")).
  If len > 0, then
- Set len to len-1
+ Set len to len-1.
  Let index be ! ToString(len).
  Return ? Set(O, index, value).
 
@@ -61,29 +61,30 @@ The SetLastArrayItem function is intentionally generic; it does not require that
 
 
 ```js
+import { ToString, ToObject, ToLength } from 'es-abstract'
 // This polyfill tries to stick as close to the spec as possible. There are polyfills which could use less code.
 Object.defineProperty(Array.prototype, 'end', {
  enumerable: false,
  configurable: false,
  get() {
- let O = Object(this)
- let len = Math.min(Math.max(0, Math.floor(Math.abs(O.length))), Number.MAX_SAFE_INTEGER)
+ let O = ToObject(this)
+ let len = ToLength(O.length)
  if (len === 0) {
  return undefined
  } else if (len > 0) {
- let newLen = len -1
- let index = String(newLen)
+ len = len -1
+ let index = ToString(len)
  let element = O[index]
  return element
  }
  },
  set(value) {
- let O = Object(this)
- let len = Math.min(Math.max(0, Math.floor(Math.abs(O.length))), Number.MAX_SAFE_INTEGER)
+ let O = ToObject(this)
+ let len = ToLength(O.length)
  if (len > 0) {
  len = len -1
  }
- let index = String(newLen)
+ let index = ToString(len)
  return O[index] = value
  },
 })