文字列接続とStringBufferの比較

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

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

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


var d1 = new Date();
var str = "";
for (var i=0; i < 10000; i++) {
    str += "text";
}
var d2 = new Date();

document.write("Concatenation with plus: "
 + (d2.getTime() - d1.getTime()) + " milliseconds");

var buffer = new StringBuffer();
d1 = new Date();
for (var i=0; i < 10000; i++) {
    buffer.append("text");
}
var result = buffer.toString();
d2 = new Date();

document.write("<br />Concatenation with StringBuffer: "
 + (d2.getTime() - d1.getTime()) + " milliseconds");

IE 6:
    Concatension with plus:79 miliseconds
    Concatension with StringBuffer:46 miliseconds
IE 7:
    Concatension with plus:78 miliseconds
    Concatension with StringBuffer:47 miliseconds
IE 8:
    Concatension with plus:0 miliseconds
    Concatension with StringBuffer:15 miliseconds
FF:
    Concatension with plus:3 miliseconds
    Concatension with StringBuffer:5 miliseconds
Opera:
    Concatension with plus:0 miliseconds
    Concatension with StringBuffer:16 miliseconds
Chrome:
    Concatension with plus:1 miliseconds
    Concatension with StringBuffer:3 miliseconds
Safari:
    Concatension with plus:1 miliseconds
    Concatension with StringBuffer:1 miliseconds