继承内置类和类的混入

继承内置类 Array是本身拥有的类

class NewArray extends Array {
    firstItem() {
        return this[0]
    }
    lastItem() {
        return this[this.length - 1]
    }
}
var arr1 = new NewArray(1, 2, 3)
console.log(arr1.firstItem());
console.log(arr1.lastItem());

 

 类的混入：在一个类添加很多相似功能

function mixineater(BaseClass) {
    return class extends BaseClass {
        eating() {
            console.log('eating');
        }
    }
}

function mixinrunner(BaseClass) {
    return class extends BaseClass {
        running() {
            console.log('runnning');
        }
    }
}
class Person {

}
class NewPerson extends mixineater(mixinrunner(Person)) {

}
var newp = new NewPerson()
newp.running()
newp.eating()