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