js的StringBuffer类

function StringBuffer(str)
{
var arr = [];
str = str || "";
arr.push(str);
this.append = function(str1)
{
arr.push(str1);
return this;
};
this.toString = function()
{
return arr.join("");
};
};

document.onreadystatechange = function(){
if(document.readyState == "complete")
{
var sb = new StringBuffer();
sb.append("Hello,").append("World");
alert(sb.toString());
}
};