我正在做一个TDD JavaScript上的ebook on GitHub,我想知道我是否遗漏了一些流行的继承模式。如果你知道任何其他的模式,我很想看看。他们应该具备以下条件:
我这样做的原因是,似乎JavaScript中的对象继承对我们中的许多人来说都很难理解。我的JavaScript继承章节基本上是对以下内容的学习帮助:克罗克福德的Good Parts和Zakas的面向网络开发人员的专业JavaScript。
以下是我到目前为止所掌握的模式:
// Pseudoclassical Inheritance
function Animal(name) {
this.name = name;
this.arr = [1,2,3];
};
Animal.prototype = {
constructor: Animal,
whoAmI: function() { return "I am " + this.name + "!\n"; }
};
function Dog(name, breed) {
this.name = name;
this.breed = breed;
};
Dog.prototype = new Animal();
Dog.prototype.getBreed = function() {
return this.breed;
};
Dog.prototype.bark = function() {
return 'ruff ruff';
};
// Combination Inheritance
function Parent(name) {
this.name = name;
this.arr = [1,2,3];
};
Parent.prototype = {
constructor: Parent,
toString: function() { return "My name is " + this.name; }
};
function Child(name, age) {
Parent.call(this, name);
this.age = age;
};
Child.prototype = new Parent();
Child.prototype.getAge = function() {
return this.age;
};
// Prototypal Inheritance
var helper = { // Thanks to Bob Vince for reminding me NOT to clobber Object!
inherit: function(p) {
NewObj = function(){};
NewObj.prototype = p;
return new NewObj();
},
inheritPrototype: function(subType, superType) {
var prototype = helper.inherit(superType.prototype);
prototype.constructor = subType;
subType.prototype = prototype;
}
};
function SubType(name, age) {
Parent.call(this, name);
this.age = age;
};
//Child.prototype = new Parent(); // Gets replaced by:
helper.inheritPrototype(SubType, Parent);
SubType.prototype.getAge = function() {
return this.age;
};
// Functional - Durable Pattern
function super_func(blueprint) {
var obj = {};
obj.getName = function() { return blueprint.name; };
obj.getAge = function() { return blueprint.age; };
obj.getFoo = function() { return blueprint.foo; };
obj.getBar = function() { return blueprint.bar; };
return obj;
};
function sub_func(blueprint) {
blueprint.name = blueprint.name || "Crockford's Place";
supr = super_func(blueprint);
supr.coolAugment = function() { return "I give a fresh new perspective on things!" };
return supr;
};
对于那些感兴趣的人,这里是jspec测试(抱歉,但Markdown或他们正在使用的任何东西会稍微破坏格式):
describe 'JavaScript Inheritance Tests'
before_each
animal = new Animal("Onyx")
dog = new Dog("Sebastian", "Lab")
person = { password : 'secret', toString : function(){ return '<Person>' } }
stub(person, 'toString').and_return('Original toString method!')
end
describe 'Pseudoclassical Inheritance Creation'
it 'should create parent and child object using pseudoclassical inheritance'
animal.constructor.should.eql Animal
// dog.constructor.should.eql Dog // Nope: expected Animal to eql Dog
dog.constructor.should.eql Animal
animal.should.be_a Animal
dog.should.be_a Animal
// dog.should.be_a Dog // Nope! We severed the original prototype pointer and now point to Animal!
dog.should.be_an_instance_of Animal
dog.should.be_an_instance_of Dog
(animal instanceof Dog).should.be_false
end
it 'should behave such that child inherits methods and instance variables defined in parent'
animal.whoAmI().should.match /I am Onyx.*/
dog.whoAmI().should.match /Sebastian.*/
animal.should.respond_to 'whoAmI'
dog.should.respond_to 'whoAmI'
dog.should.have_prop 'name'
end
it 'should behave such that methods and instance variables added to child are NOT available to parent'
dog.bark().should.match /Ruff Ruff/i
dog.should.have_property 'breed'
dog.should.respond_to 'bark'
// animal.should.have_prop 'breed' // Of course not!
// animal.should.respond_to 'bark' // Of course not!
end
it 'should behave such that reference variables on the parent are "staticy" to all child instances'
dog.arr.should.eql([1,2,3])
dog.arr.push(4)
dog.arr.should.eql([1,2,3,4])
spike = new Dog("Spike", "Pitbull")
spike.arr.should.eql([1,2,3,4])
spike.arr.push(5)
rover = new Dog("Rover", "German Sheppard")
spike.arr.should.eql([1,2,3,4,5])
rover.arr.should.eql([1,2,3,4,5])
dog.arr.should.eql([1,2,3,4,5])
end
end
describe 'Combination Inheritance Solves Static Prototype Properties Issue'
it 'should maintain separate state for each child object'
child_1 = new Child("David", 21)
child_2 = new Child("Peter", 32)
child_1.arr.push(999)
child_2.arr.push(333)
child_1.arr.should.eql([1,2,3,999])
child_2.arr.should.eql([1,2,3,333])
child_1.getAge().should.eql 21
child_1.should.be_a Parent
end
end
describe 'Prototypal Inheritance'
it 'should inherit properties from parent'
person.toString().should.match /Original toString.*/i
person.password.should.eql 'secret'
joe = helper.inherit(person)
joe.password.should.eql 'secret'
joe.password = 'letmein'
joe.password.should.eql 'letmein'
person.password.should.eql 'secret'
end
end
describe 'Parisitic Combination Inheritance'
it 'should use inheritPrototype (to call parent constructor once) and still work as expected'
sub = new SubType("Nicholas Zakas", 29)
sub.toString().should.match /.*Nicholas Zakas/
sub.getAge().should.eql 29
charlie = new SubType("Charlie Brown", 69)
charlie.arr.should.eql([1,2,3])
charlie.arr.push(999)
charlie.arr.should.eql([1,2,3,999])
sub.arr.should.eql([1,2,3])
sub.should.be_an_instance_of SubType
charlie.should.be_an_instance_of SubType
(sub instanceof SubType).should.eql true
(sub instanceof Parent).should.eql true
end
end
describe 'Functional Durable Inheritance'
it 'should hide private variables'
sup = new super_func( {name: "Superfly Douglas", age: 39, foo: "foo", bar: "bar"} )
sup.getName().should.eql 'Superfly Douglas'
sup.name.should.be_undefined
sup.getAge().should.eql 39
sup.age.should.be_undefined
sup.getFoo().should.eql 'foo'
sup.foo.should.be_undefined
end
it 'should create a descendent object that inherits properties while maintaining privacy'
sub = new sub_func( {name: "Submarine", age: 1, foo: "food", bar: "barfly"} )
sub.getName().should.eql 'Submarine'
sub.name.should.be_undefined
sub.getAge().should.eql 1
sub.age.should.be_undefined
sub.getFoo().should.eql 'food'
sub.foo.should.be_undefined
sub.getBar().should.eql 'barfly'
sub.bar.should.be_undefined
sub.coolAugment().should.match /.*fresh new perspective.*/
//sub.should.be_an_instance_of super_func NOPE!
//sub.should.be_an_instance_of sub_func NOPE!
sub.should.be_an_instance_of Object
end
end
end
谢谢大家!哦,如果你想看看我的论文/书,我很乐意得到反馈:TDD JavaScript at GitHub repo
发布于 2009-10-30 00:55:31
有关摘要,请参阅How to "properly" create a custom object in JavaScript?。(既然我花了太多时间把它打出来,不妨把它链接起来!)
这一点:
Dog.prototype =新动物();
通常会被避免。你可以在示例/教程代码中看到它,但它是一个可怕的混乱,因为它将一个类建立在一个实例上,而一个实例是以错误的方式构造的:name
是未定义的。任何更复杂的构造函数都会对这类事情感到不安。
Object.prototype.inherit=
是一种更好的构造方法,但将任何东西原型化为Object
都被认为是非常糟糕的。它冒着将对象用作微不足道的映射并破坏其他代码的风险。你可以把这个辅助函数放在别的地方,例如。Function.prototype.subclass
。
prototype.constructor
就我个人而言,我倾向于避免,因为constructor
在JavaScript中有一个特殊的含义(就像在火狐和其他浏览器中实现的那样;而不是IE的JScript),这个含义既不是constructor
在这里做的,也不是你期望任何这样的属性做的;它令人困惑,而且几乎总是最好避免的。因此,如果在类系统中的实例中包含到构造函数的链接,我更愿意给它命名为其他名称。
发布于 2010-12-15 08:56:10
我以前公司的一位同事开发了一个类似于继承http://www.uselesspickles.com/class_library/的java库。我认为它比Rajendra的建议更性感,语法看起来更干净。
我写了一篇文章,演示了不同的方法来处理它,但要确保避免已知的不良实践。http://js-bits.blogspot.com/2010/08/javascript-inheritance-done-right.html,如果你不想下载一个库,而只是想复制粘贴一些代码,你可以改进这些代码来做你需要的事情。
发布于 2012-11-26 10:41:21
这里值得一提的是一个有趣的模式: JavaScript构造函数可以返回任何对象(这不是必须的)。可以创建一个构造函数,它返回一个代理对象,其中包含"real“实例对象的"real”方法的代理方法。这听起来可能很复杂,但并不复杂;以下是一段代码片段:
var MyClass = function() {
var instanceObj = this;
var proxyObj = {
myPublicMethod: function() {
return instanceObj.myPublicMethod.apply(instanceObj, arguments);
}
}
return proxyObj;
};
MyClass.prototype = {
_myPrivateMethod: function() {
...
},
myPublicMethod: function() {
...
}
};
好的是,如果我们定义一个命名受保护方法的约定,就可以自动创建代理。我创建了一个小库来做这件事:http://idya.github.com/oolib/
https://stackoverflow.com/questions/1645027
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