JavaScript 函数返回未定义 + 控制台日志

Question

有人可以帮我修复我的千树（）函数，它显示我想要的控制台日志，但它也在控制台上返回 undefined 。

我如何使该功能只执行控制台日志？

这是我正在学习的课程练习的一部分。

该功能就在代码的底部

谢谢你

// park constructor
class Park {
    constructor (name, buildYear, trees, size) {
        this.name = name;
        this.buildYear = buildYear;
        this.trees = trees;
        this.size = size;
    }

    // number of tree / park area
    treeDensity() {
        return this.trees / this.size;
    }

    // return the park age
    parkAge() {
        return new Date().getFullYear() - this.buildYear;
    }
}

// street constructor
class Street {
    constructor (name, buildYear, size) {
        this.name = name;
        this.buildYear = buildYear;
        this.size = size;
    }
};


// all parks

let allParks = [
    park1 = new Park("Brighton Park", 1900, 1200, 3),
    park2 = new Park("Worthing Park", 1800, 650, 2),
    park3 = new Park("Shoreham Park", 1850, 350, 2)
]
// all streets

let allStreets = [
    street1 = new Street("Brighton Street", 1858, 2000),
    street2 = new Street("Worthing Street", 1950, 1200),
    street3 = new Street("Shoreham Street", 1850, 800),
    street4 = new Street("Lancing Street", 1980, 760)
];

// calculate the average age of all parks
let parkAgeAvg = function() {
    return (park1.parkAge() + park2.parkAge() + park3.parkAge()) / 3
};
// Display the name of the park with more than 1000 trees
let thousandTrees = function() {
    for (let cur of allParks) {
        if (cur.trees >= 1000) {
          console.log(`${cur.name} has more than 1000 trees, we have verified there is actually ${cur.trees} trees in total.`);
        }
    }
};

// total length of streets and avg length

//size classification of all streets

Answer 1

在 chrome 中，我在 console.log 中没有看到任何错误

 // park constructor class Park { constructor (name, buildYear, trees, size) { this.name = name; this.buildYear = buildYear; this.trees = trees; this.size = size; } // number of tree / park area treeDensity() { return this.trees / this.size; } // return the park age parkAge() { return new Date().getFullYear() - this.buildYear; } } // street constructor class Street { constructor (name, buildYear, size) { this.name = name; this.buildYear = buildYear; this.size = size; } }; // all parks let allParks = [ park1 = new Park("Brighton Park", 1900, 1200, 3), park2 = new Park("Worthing Park", 1800, 650, 2), park3 = new Park("Shoreham Park", 1850, 350, 2) ] // all streets let allStreets = [ street1 = new Street("Brighton Street", 1858, 2000), street2 = new Street("Worthing Street", 1950, 1200), street3 = new Street("Shoreham Street", 1850, 800), street4 = new Street("Lancing Street", 1980, 760) ]; // calculate the average age of all parks let parkAgeAvg = function() { return (park1.parkAge() + park2.parkAge() + park3.parkAge()) / 3 }; // Display the name of the park with more than 1000 trees let thousandTrees = function() { for (let cur of allParks) { if (cur.trees >= 300) { console.log(`${cur.name} has more than 1000 trees, we have verified there is actually ${cur.trees} trees in total.`); } } }; thousandTrees();

Answer 2

您看到的undefined只是因为您在控制台中调用的函数返回undefined ，并且您在控制台中评估的任何 JS 都会显示表达式的值。 它与控制台日志代码无关。

旁注，您如何初始化事物存在问题：

let allParks = [
    park1 = new Park("Brighton Park", 1900, 1200, 3),
    park2 = new Park("Worthing Park", 1800, 650, 2),
    park3 = new Park("Shoreham Park", 1850, 350, 2)
]

在某些模式下，JavaScript 会对此park1窒息，因为park1 、 park2和park3是未定义的。 我相信你真正想要的只是：

let allParks = [
    new Park("Brighton Park", 1900, 1200, 3),
    new Park("Worthing Park", 1800, 650, 2),
    new Park("Shoreham Park", 1850, 350, 2)
]

在前者中，您使用赋值表达式的结果填充数组。 在第二个中，你用构造的对象填充它。

allStreets反馈相同。

Answer 3

定义您在数组中使用的变量：

// all parks
let park1,park2,park3;

let allParks = [
     park1 = new Park("Brighton Park", 1900, 1200, 3),
     park2 = new Park("Worthing Park", 1800, 650, 2),
     park3 = new Park("Shoreham Park", 1850, 350, 2)
]
// all streets
let street1, street2, street3, street4;

let allStreets = [
    street1 = new Street("Brighton Street", 1858, 2000),
    street2 = new Street("Worthing Street", 1950, 1200),
    street3 = new Street("Shoreham Street", 1850, 800),
    street4 = new Street("Lancing Street", 1980, 760)
];