在对象内部，一个方法可以使用另一个方法的返回值吗？

Question

在下面的测试代码中，工厂函数创建了一个对象。新对象内部有 2 个方法，totalCost 和 withShipping。有没有我可以使用的模式允许withShipping 使用totalCost 的返回值？按照配置，它会引发错误。非常感谢您的帮助！

"use strict"

function factoryTest(x) {
    let returnTest = {
        numberOfEngines: x.numberOfEngines,
        costPerEngine: x.costPerEngine,
        totalCost: function() {
            return x.numberOfEngines * x.costPerEngine;
        },
        withShipping: function() {
            return x.totalCost() * 2;
        }

    }
    return returnTest;
}

let aircraft = factoryTest({numberOfEngines: 2, costPerEngine: 40000});

console.log(aircraft.totalCost());
console.log(aircraft.withShipping());

Answer 1

最简单的方法是使用this 访问当前实例化：

"use strict"

function factoryTest(x) {
    let returnTest = {
        numberOfEngines: x.numberOfEngines,
        costPerEngine: x.costPerEngine,
        totalCost: function() {
            return x.numberOfEngines * x.costPerEngine;
        },
        withShipping: function() {
            return this.totalCost() * 2;
        }

    }
    return returnTest;
}

let aircraft = factoryTest({numberOfEngines: 2, costPerEngine: 40000});

console.log(aircraft.totalCost());
console.log(aircraft.withShipping());

由于您使用的是工厂函数模式，另一种可行的方法是定义totalCost 函数以及returnTest 之外的所有其他 函数，然后调用它：

"use strict"

function factoryTest({
  numberOfEngines,
  costPerEngine
}) {
  const totalCost = () => numberOfEngines * costPerEngine;
  return {
    numberOfEngines,
    costPerEngine,
    totalCost,
    withShipping: () => totalCost() * 2,
  };
}

const aircraft = factoryTest({
  numberOfEngines: 2,
  costPerEngine: 40000
});

console.log(aircraft.totalCost());
console.log(aircraft.withShipping());