TypeError：不是继承对象函数的函数

Question

我只是想用简单的代码来理解原型继承。

function Place() {

}

Place.prototype.airportCode = function(code) {
    console.log('Airport code is: ' + code);
}

function City(cityName) {
    this.name = cityName;
}

City.prototype.railwayStateCode = function(code) {
    console.log('Railway station code is: ' + code);
}

City.prototype = Object.create(Place.prototype);

const sydney = new City('Sydney');

const melbourne = new Place();

当我尝试时

sydney.railwayStateCode('SYD');

我收到一个错误

TypeError: sydney.railwayStateCode is not a function

根据我的理解，它不应该抛出错误。我做错了吗？

Answer 1

你在这里覆盖了原型：

City.prototype = Object.create(Place.prototype);

要使其正常工作，请按如下方式更改顺序：

City.prototype = Object.create(Place.prototype);

City.prototype.railwayStateCode = function(code) {
    console.log('Railway station code is: ' + code);
}