​x
 
<html>
<body>
​
<script type="text/javascript">
​
function StringBuffer () {
  this._strings_ = new Array();
}
​
StringBuffer.prototype.append = function(str) {
  this._strings_.push(str);
};
​
StringBuffer.prototype.toString = function() {
  return this._strings_.join("");
};
​
var buffer = new StringBuffer ();
buffer.append("hello ");
buffer.append("world");
var result = buffer.toString();
​
document.write(buffer);
​
</script>
​
</body>
</html>
​