TypeScript接口继承多个类后调用方法报not a function如何解决

• TypeScript中接口继承类时，仅会继承类的成员类型定义，不会继承任何实际运行时的实现逻辑
• 你自定义的Employee类虽然声明了实现同时继承Person、Animal的Employee接口，但没有手动实现eat、speak等方法，也没有将两个父类的原型方法混入到Employee类中，运行时自然找不到对应方法抛出错误。

TypeScript官方推荐通过混入（Mixin）模式实现类似多继承的能力，实现代码如下：

class Animal {
    species: string;
    id: number = 0;
    constructor(species: string) {
        this.species = species
    }
    eat(fruit:string):void{
        console.log('eating is healthy ' + fruit)
    }
}
class Person {
    name: string;
    id: number = 0;
    constructor(name: string) {
        this.name = name
    }
    speak(){
        console.log(this.name + this.id);
    }
}

// 定义Employee接口合并两个父类的类型
interface Employee extends Person, Animal {    
    employeeCode: string;
}

// 实现Employee类，只写自身独有的属性和方法
class Employee {
    employeeCode: string = '';
    constructor(name: string, species: string, code: string) {
        // 手动调用两个父类的构造函数初始化属性
        Object.assign(this, new Person(name), new Animal(species));
        this.employeeCode = code;
    }
}

// 混入辅助函数，把父类的原型方法复制到子类原型上
function applyMixins(derivedCtor: any, constructors: any[]) {
  constructors.forEach((baseCtor) => {
    Object.getOwnPropertyNames(baseCtor.prototype).forEach((name) => {
      Object.defineProperty(
        derivedCtor.prototype,
        name,
        Object.getOwnPropertyDescriptor(baseCtor.prototype, name) ||
          Object.create(null)
      );
    });
  });
}

// 执行混入，将Person和Animal的方法混入到Employee
applyMixins(Employee, [Person, Animal]);

// 测试运行
let employee: Employee = new Employee('张三', '智人', 'E001');
employee.eat('apple'); // 正常输出 eating is healthy apple
employee.speak(); // 正常输出 张三0

内容的提问来源于stack exchange，提问作者user2024080