TypeScript 类的普通成员函数获取不到

Question

ts官方文档里交叉类型这一节

function extend<T, U>(first: T, second: U): T & U {
  console.log(first, second);
  let result = <T & U>{};
  for (let id in first) {
    (<any>result)[id] = (<any>first)[id];
  }
  for (let id in second) {
    if (!result.hasOwnProperty(id)) {
      (<any>result)[id] = (<any>second)[id];
    }
  }

  return result;
}

class Person {
  constructor(public name: string) {}
}

interface Loggable {
  log(): void;
}

class ConsoleLogger implements Loggable {
  //   log() {} //这样写 没有这个属性
  log = () => {
    console.log('ConsoleLogger implements Loggable...');
  };
}

var jim = extend(new Person('Jim'), new ConsoleLogger());
console.log(jim);
var n = jim.name;
jim.log();

这么写，直接使用ts-node运行时报错jim.log is not a function
换成匿名函数写法可以获取到log属性

class ConsoleLogger implements Loggable { 
  log=()=> { // ... } 
}
...
jim.log();

这两种写法编译成.js后都能成功执行
ts版本：3.7.4
ts-node: 8.5.4

请问是什么原因~~~~