Question

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有人可以帮助我修复我的MillenniumTrees（）函数，该函数显示我想要的控制台日志，但是在控制台上也返回undefined。

我如何使功能仅在控制台日志中显示？

这是我正在学习的课程的一部分练习。

该函数位于代码的底部

谢谢

// 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，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仅仅是因为您正在控制台中调用的函数返回 undefined，并且您在控制台中评估的所有JS都会显示该值的表达。它与控制台记录代码无关。

旁注，您在初始化事物时存在问题：

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可能会阻塞，因为park1，park2和park3是未定义的。我相信您真正想要的只是：

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

在前一种方法中，您要用赋值表达式的结果填充数组。在第二个中，您要用构造的对象填充它。

对allStreets的反馈意见相同。

Answer 3

定义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)
];

JavaScript函数返回未定义+控制台日志

3 个答案: