es6.array.copy-within.js

'use strict';
var $def     = require('./$.def')
  , toObject = require('./$.to-object')
  , toIndex  = require('./$.to-index')
  , toLength = require('./$.to-length');
$def($def.P, 'Array', {
  // 22.1.3.3 Array.prototype.copyWithin(target, start, end = this.length)
  copyWithin: function copyWithin(target/* = 0 */, start /* = 0, end = @length */){
    var O     = toObject(this)
      , len   = toLength(O.length)
      , to    = toIndex(target, len)
      , from  = toIndex(start, len)
      , end   = arguments[2]
      , fin   = end === undefined ? len : toIndex(end, len)
      , count = Math.min(fin - from, len - to)
      , inc   = 1;
    if(from < to && to < from + count){
      inc  = -1;
      from = from + count - 1;
      to   = to   + count - 1;
    }
    while(count-- > 0){
      if(from in O)O[to] = O[from];
      else delete O[to];
      to   += inc;
      from += inc;
    } return O;
  }
});
require('./$.unscope')('copyWithin');