什麼是prototype呢？看書，GOOGLE之，還問了一隻很特別的鳥，學到了一點點，如下面的小執行個體：
<html>
<script lang="text/javascript">
function father(){
this.plus_other = function(){
alert('plus_other: ' + this.cityId);
}
}
function City(){
this.plus_other = function(){
alert('plus_other!');
}
}
function City2(){}
City.prototype = father;
City2.prototype = father;
City.prototype.plus = function(){
alert('plus!');
}
var city1 = new City();
city1.plus_other();
var city2 = new City2();
//city2.plus_other(); 沒有這個方法，所以這行會報錯
city.plus();
</script>
</body>
</html>
其實prototype（原型）就是類似於基類……，而使用 “某對象A.prototype.XXX” 的方法就是把新的方法或者屬性定義到 “A對象”的原型（類似於父類、基類）中去。所以city2對象也有plus方法，但是city2對象沒有plus_other方法。
prototype還有什麼好玩的特性呢？……學習研究中……
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