利用__define_setter__和 __define_getter__ 定义动态的对象属性

var obj = {
get foo() {
return Math.random() > 0.5 ? 'foo' : 'bar';
}
};
var sum = '';
for(var i=1; i<10; i++) {
sum += obj.foo + "\n"; //'foo' or 'bar' randomly ?
}
alert(sum);

function Tester(str) {

var colors = {
red : ['red_', '_r'],
green : ['red_', '_r'],
gray : ['gray_', '_g']
};

var self = this;

for(var i in colors) {
var ars = colors[i];
self.__defineGetter__(i, function() {
var rs = ars[0] + str + ars[1];
return rs;
});
}
}

var t = new Tester("Hello!");
alert(t.red);