JavaScript语言精粹之继承篇

1.伪类 构造器继承

var Person = function (name) {
    this.name = name;
}
Person.prototype.getName = function () {
    return this.name;
}
Person.prototype.getSaying = function () {
    return this.saying || "";
}
var p = new Person("zhang");
alert(p.getName()); // zhang
var Student = function (name) {
    this.name = name;
    this.saying = "student saying";
}
Student.prototype = new Person();
Student.prototype.purr = function (n) {
    var i, s = '';
    for(i = 0; i < n; i++) {
        if(s) {
            s += "-";
        }
        s += "r";
    }
    return s;
}
var s = new Student("li");
alert(s.getSaying());   // sayistudent
alert(s.purr(10));  // r-r-r-r-r-r-r-r-r-r

伪类模式的本意是向面向对象靠拢，但是看起来总是格格不入，我们可以优化一个

Function.prototype.method = function (name, func) {
    if (! this.prototype[name]) {
        this.prototype[name] = func;
    }
    return this;
}
Function.method("inherits", function (Parent) {
    this.prototype = new Parent();
    return this;
});
var Teacher = function (name) {
    this.name = name;
    this.saying = "teacher saying";
}
.inherits(Person)
.method("purr", function (n) {
    var i, s = '';
    for(i = 0; i < n; i++) {
        if(s) {
            s += "-";
        }
        s += "r";
    }
    return s;
})
.method("getName", function (){
    return this.getSaying() + " " + this.name + this.getSaying();   
});
var t = new Teacher("wang");
alert(t.getName()); // wang
alert(t.purr(3));       // r-r-r

缺陷
没有私有环境
所有的属性都是公开的
无法访问super父类的方法
在实例化时，如果忘记new，那么this会指向全局环境
2.对象说明符
有时候，实例化构造器时会有许多参数，我们会感觉很麻烦

var myObject = maker(f, l, s, c);

因此我们可以如下面来，使用对象说明符

var myObject = maker({
    first : f,
    last : l,
    state : s,
    city : c
});

这样我们就可以很清晰的看清楚了参数的顺序关系了
对象说明符和JSON结合使用有意想不到的便捷
3.原型
让我们用对象字面量的形式创建一个有用的对象

var myPerson = {
    name : "hello everyone",
    getName : function() {
        return this.name;
    },
    says : function () {
        return this.saying || "";
    }
}
Object.prototype.create = function (o) {
    if(typeof Object.create !== "function") {
        Object.create = function () {
            var F = function () {};
            F.prototype = o;
            return new F();
        }
    }
}
var worker = Object.create(myPerson);
worker.name = "worker";
worker.saying = "saying";
worker.getSaying = function () {
    return this.name + " " + this.saying;
}
alert(worker.getSaying());  // worker saying
alert(myPerson.getName());      // hello everyone

4.函数化
迄今为止，我们所有的继承的方式都无法保护隐私，我们可以用模式的方式来解决

var mammal = function (spec) {
    var that = {};
    that.getName = function () {
        return spec.name;
    };
    that.getSaying = function () {
        return spec.saying || "";
    }
    return that;
}
var m = mammal({name : "zhang"});
alert(m.name);  // undefined
alert(m.getName()); // zhang

让cat继承mammal

Function.prototype.method = function (name, func) {
    if(this.prototype[name] !== "function") {
        this.prototype[name] = func;
    }
    return this;
}
var cat = function(spec) {
    spec.saying = spec.saying || "";
    var that = mammal(spec);
    override getName method
    that.getName = function () {
        return spec.name + " : " + spec.saying;
    };
    that.purr = function (n) {
        var i, s = '';
        for(i = 0; i < n; i++) {
            if(s) {
                s += "-";
            }
            s += "r";
        }
        return s;
    }
    return that;
}
var c = cat({name : "wang", saying : "hello dear"});
alert(c.getName()); // wang : hello dear
alert(c.purr(3));       // r-r-r
// 调用父类的方法
Object.method("superior", function (name) {
    var that = this,
        method = that[name];
    return function () {
        return method.apply(that, arguments);
    }
});
var littleCat = function (spec) {
    var that = cat(spec);
    get_super_name = that.superior("getName");
    that.getName = function () {
        return "like " + get_super_name() + " body";
    }
    return that;
}
var lc = littleCat({name : "zhangFei", saying : "Come On"});
alert(lc.getName());    // like zhangFei : Come On body

5.部件

var eventuality = function (that) {
    var registry = {};
    that.fire = function (event) {
        // alert(event.type); // show
        var array, func, handler, i,
            type = typeof event === "string" ? event : event.type;
        if(registry.hasOwnProperty(type)) {
            array = registry[type];
            // alert(array); // [object Object]
            for(i = 0; i < array.length; i++) {
                handler = array[i];
                // alert(handler); // [object Object]
                func = handler.method;
                // alert(func()); // show
                if (typeof func === 'string') {
                    func = this[func];
                }
                func.apply(this, handler.parameters || [event]);
            }
        }
        return this;
    }
    that.on = function (type, method, parameters) {
        var handler = {
            method : method, 
            parameters : parameters
        };
        // handler = {
            // method : "show",
            // parameters : [1, 2, 3]
        // }
        if(registry.hasOwnProperty(type)) {
            registry[type].push(handler);
        } else {
            registry[type] = [handler];
        }
        // alert(registry[type][0].method()); // show
        // alert(registry[type][0].parameters); // 1, 2, 3

        return this;
    }
    return that;
}
var e = eventuality({ name : "zhang"});
var show = function () {
    return "show";
}
e.on("show", show, [1, 2, 3]);
e.fire({type : "show"});