JavaScript 字符串连接

function StringBuffer () {
  this._strings_ = new Array();
}

StringBuffer.prototype.append = function(str) {
  this._strings_.push(str);
};

StringBuffer.prototype.toString = function() {
  return this._strings_.join("");
};

var str = new StringBuffer();
str.append("Audi");
str.append("BMW");
str.append("Saab");

实际测试的时候，发现居然 用 + 连接字符串性能更好？
测试代码

var d1 = new Date();
var str = "";
for (var i=0; i < 60000; i++) {
    str += "text";
}
var d2 = new Date();
document.write("Concatenation with plus: " + (d2.getTime() - d1.getTime()) + " milliseconds <br/>");

var buffer = new StringBuffer();
d1 = new Date();
for (var i=0; i < 60000; i++) {
    buffer.append("text");
}
var result = buffer.toString();
d2 = new Date();
document.write("Concatenation with StringBuffer: "  + (d2.getTime() - d1.getTime()) + " milliseconds <br/>");

prt(str.length + "-" + result.length);

输出结果

Concatenation with plus: 47 milliseconds 
Concatenation with StringBuffer: 141 milliseconds