js 实现继承相关

☊ 【要求】：实现一个Animal类, 和一个继承它的Dog类

☛ 【实现】：

function Animal(name) {
	this.name = name;
}

Animal.prototype.cry = function() {
	console.log('I am ' + this.name);
}

function Dog(name) {
	Animal.call(this, name);
	this.hobby = 'running';
}

Dog.prototype = new Animal();

// 注意要放在上条语句的下面
Dog.prototype.run = function() {
	console.log('I like ' + this.hobby);
}

var dog = new Dog('doggy');
dog.run();	// 'I like running'
dog.cry();	// 'I am doggy'

---

☊ 【要求】：用JS实现一个类继承函数

function extend(parent){ /*...*/}

☛ 【实现】：

function Animal(name) {
	this.name = name;
}

Animal.prototype.cry = function() {
	console.log('I am ' + this.name);
}

var People = {
	name: 'bb',
	say: function() {
		console.log(this.name);
	}
}

function extend(parent) {

	if (typeof parent == 'function') {
		function child() {
			parent.call(this, ...arguments);
		}

		// 可以在 child 的原型上自己定义方法，而不会影响 parent 的原型
		child.prototype = new parent();
	}

	if (typeof parent == 'object') {
		function child() {};

		// 将 parent 作为 child 的原型
		child.prototype = parent;
	}
	
	return child;
}

var Pet = extend(Animal);
var dog = new Pet('doggy'); // child {name: "doggy"}
dog.name = 'Doggy';
dog.cry();	// 'I am Doggy'

var Person = extend(People);
var bob = new Person;   // child {name: "Bob"}
bob.name = 'Bob';
bob.say();	// 'Bob'