javascript - 我怎样才能得到一个构造函数的值给其他方法修改呢？

Question

该项目的目标是重构以前的解决方案以使用实际对象。目前，当我运行 Jasmine 测试时，出现以下两个错误:

TypeError: 无法读取未定义的属性 'split'

类型错误:无法设置未定义的属性“标题”

为什么当我尝试将标题值传递给其他方法时，该类无法识别标题值？在我尝试将值发送到其他方法之前，它似乎可以工作，但现在我尝试将字符串值发送到 titleCreator 方法时，它一直返回未定义。

class bookTitle {
    constructor(title) {
        this.title = this.titleCreator(title); // this sets a title value to the bookTitle object/class
    }

    titleCreator(string) {
        // Note that this isn't meant to be a fully fledged title creator, just designed to pass these specific tests
        var littleWords = ["and", "over", "the"]; // These are the words that we don't want to capitalize

        var modifiedString = this.string
        .split(' ') // Splits string into array of words, basically breaks up the sentence
        .map(function(word,index) {
            if (index == 0) {
                return capitalize(word); // capitalize the first word of the string
            } else if (littleWords.indexOf(word) == -1) {
                return capitalize(word); // capitalize any words that are not little, the -1 is returned by indexOf if it can't find the word in the array
            } else if (littleWords.indexOf(word) >= 0) {
                return word; // do not capitalize as this word is in the list of littleWords
            }
        })
        .join(' '); // Joins every element of an array into a string with a space inbetween each value. Basically you created a sentence from an array of words

        return modifiedString;

    }

    capitalize(word) {
        return word.charAt(0).toUpperCase() + word.slice(1);
        // This function just capitalizes the word given to it
    }
}

module.exports = {
    bookTitle
}

编辑:这是我的 Jasmine 上下文测试用例。该程序的想法就是通过这些案例

var bookTitles = require ('./bookTitles.js');

describe('bookTitle', function() {

    var book; // this is the object that will be passed into the test cases, returns undefined here without beforeEach

    beforeEach(function() {
        book = new bookTitles.bookTitle(); // creates a new book instance before each test is run
    });

    describe('title', function() {
        it('should capitalize the first letter', function() {
            book.title = 'inferno';
            expect(book.title).toEqual('Inferno'); // works without capitalizing
        });

        it('should capitalize every word', function() {
            book.title = 'stuart little';
            expect(book.title).toEqual('Stuart Little');
        });

        describe('should capitalize every word except...', function() {
            describe('articles', function() {
                it('does not capitalize "the"', function() {
                    book.title = 'alexander the great';
                    expect(book.title).toEqual('Alexander the Great');
                });

                it('does not capitalize "a"', function() {
                    book.title = 'to kill a mockingbird';
                    expect(book.title).toEqual('To Kill a Mockingbird');
                });

                it('does not capitalize "an"', function() {
                    book.title = 'to eat an apple a day';
                    expect(book.title).toEqual('To Eat an Apple a Day');
                });
            });

            it('conjunctions', function() {
                book.title = 'war and peace';
                expect(book.title).toEqual('War and Peace');
            });

            it('prepositions', function() {
                book.title = 'love in the time of cholera';
                expect(book.title).toEqual('Love in the Time of Cholera');
            });
        });

        describe('should always capitalize...', function() {
            it('I', function() {
                book.title = 'what i wish i knew when i was 20';
                expect(book.title).toEqual('What I Wish I Knew When I Was 20');
            });

            it('the first word', function() {
                book.title = 'the man in the iron mask';
                expect(book.title).toEqual('The Man in the Iron Mask');
            });
        });
    });
});

Answer 1

您正试图在这行代码中访问 this.string:

var modifiedString = this.string

在将 this.string 设置为具有任何值之前。也许您只想使用 string，即传递给 titleCreator 的参数。 this.string 与 string 不同。由于 this.string 从未被赋值，因此它是 undefined，因此任何尝试访问它的方法都会失败。

很难确切地知道您的意图是什么，但也许您打算使用 string 而不是 this.string:

titleCreator(string) {
    // Note that this isn't meant to be a fully fledged title creator, just designed to pass these specific tests
    var littleWords = ["and", "over", "the"]; // These are the words that we don't want to capitalize

    var modifiedString = string
      .split(' ') // Splits string into array of words, basically breaks up the sentence
      .map(function(word,index) {
        if (index == 0) {
            return capitalize(word); // capitalize the first word of the string
        } else if (littleWords.indexOf(word) == -1) {
            return capitalize(word); // capitalize any words that are not little, the -1 is returned by indexOf if it can't find the word in the array
        } else if (littleWords.indexOf(word) >= 0) {
            return word; // do not capitalize as this word is in the list of littleWords
        }
    })
    .join(' '); // Joins every element of an array into a string with a space inbetween each value. Basically you created a sentence from an array of words

    return modifiedString;
}

根据您的错误描述，听起来您可能对调用 bookTitle 的方式有疑问(它应该像在

中一样作为构造函数调用

let bk = new (yourModule.bookTitle)("some string") 

如果您需要这方面的帮助，请显示调用该构造函数的调用代码，以便我们也可以就此提出建议。

---

这是一段工作代码，我必须在其中修复其他几个问题:

    class bookTitle {
        constructor(title) {
            this.title = this.titleCreator(title); // this sets a title value to the bookTitle object/class
        }
    
        titleCreator(string) {
            // Note that this isn't meant to be a fully fledged title creator, just designed to pass these specific tests
            var littleWords = ["and", "over", "the"]; // These are the words that we don't want to capitalize
            
            var self = this;
    
            var modifiedString = string
            .split(' ') // Splits string into array of words, basically breaks up the sentence
            .map(function(word,index) {
                if (index == 0) {
                    return self.capitalize(word); // capitalize the first word of the string
                } else if (littleWords.indexOf(word) == -1) {
                    return self.capitalize(word); // capitalize any words that are not little, the -1 is returned by indexOf if it can't find the word in the array
                } else if (littleWords.indexOf(word) >= 0) {
                    return word; // do not capitalize as this word is in the list of littleWords
                }
            })
            .join(' '); // Joins every element of an array into a string with a space inbetween each value. Basically you created a sentence from an array of words
    
            return modifiedString;
    
        }
    
        capitalize(word) {
            return word.charAt(0).toUpperCase() + word.slice(1);
            // This function just capitalizes the word given to it
        }
    }
    
    let bookTitles = {
        bookTitle: bookTitle
    };
    
    let book = new bookTitles.bookTitle("some title of the book");
    console.log(book)

我必须解决的问题:

1. 将 this.string.split(...) 更改为 string.split(...)。
2. 将 self 定义为 this。
3. 使用 self.capitalize() 而不是 capitalize() 来正确调用方法(在两个地方)
4. 调用构造函数时传入一个字符串(您的代码调用构造函数时没有参数，这会在构造函数中出错)。您的代码需要将字符串传递给构造函数。

此外，您的代码似乎认为仅分配给 .title 属性将以某种方式运行 titleCreator() 方法并进行适当的大写。它不会。分配给 .title 属性只是设置该属性。它不会运行您的任何方法。您可以定义一个 setter 方法，使其在您分配给该属性时运行代码，但是创建一个 setTitle() 方法来执行您想要的操作(调用 .titleCreator() 并将结果分配给 .title)。