js实现继承方式
原型链继承
通过将子类的原型指向父类的实例实现继承。子类实例通过原型链访问父类属性和方法。
function Parent() {
this.name = 'parent';
}
Parent.prototype.sayName = function() {
console.log(this.name);
};
function Child() {}
Child.prototype = new Parent();
const child = new Child();
child.sayName(); // 'parent'构造函数继承
在子类构造函数中调用父类构造函数，通过call/apply方法改变this指向。
function Parent(name) {
this.name = name;
}
function Child(name) {
Parent.call(this, name);
}
const child = new Child('child');
console.log(child.name); // 'child'组合继承
结合原型链继承和构造函数继承，既通过原型链继承方法，又通过构造函数继承属性。
function Parent(name) {
this.name = name;
}
Parent.prototype.sayName = function() {
console.log(this.name);
};
function Child(name) {
Parent.call(this, name);
}
Child.prototype = new Parent();
const child = new Child('child');
child.sayName(); // 'child'原型式继承
基于已有对象创建新对象，Object.create()方法实现类似效果。
const parent = {
name: 'parent',
sayName: function() {
console.log(this.name);
}
};
const child = Object.create(parent);
child.name = 'child';
child.sayName(); // 'child'寄生式继承
在原型式继承基础上增强对象，添加额外方法。
function createChild(parent) {
const child = Object.create(parent);
child.sayHello = function() {
console.log('hello');
};
return child;
}
const parent = { name: 'parent' };
const child = createChild(parent);
child.sayHello(); // 'hello'寄生组合式继承
最理想的继承方式，避免组合继承中两次调用父类构造函数的问题。
function inheritPrototype(child, parent) {
const prototype = Object.create(parent.prototype);
prototype.constructor = child;
child.prototype = prototype;
}
function Parent(name) {
this.name = name;
}
Parent.prototype.sayName = function() {
console.log(this.name);
};
function Child(name) {
Parent.call(this, name);
}
inheritPrototype(Child, Parent);
const child = new Child('child');
child.sayName(); // 'child'ES6类继承
使用class和extends语法糖实现继承，底层仍是基于原型链。
class Parent {
constructor(name) {
this.name = name;
}
sayName() {
console.log(this.name);
}
}
class Child extends Parent {
constructor(name) {
super(name);
}
}
const child = new Child('child');
child.sayName(); // 'child'
