实例化函数多参数的实现方式

con_muil_arg.js

var _no_new = {};
var Cons = function (arg) {
	if (!(this instanceof Cons)) {
		var instance = new Cons(_no_new);
		instance._init.apply(instance,arguments);
		return instance;
	}
	if (arg !== _no_new) {
		this._init.apply(this,arguments);
	}
}
Cons.prototype._init = function(a,b,c) {
	a&&(this.a = a);
	b&&(this.b = b);
	c&&(this.c = c);
};