javascript - JS如何创建一个计算主题标签数量的函数

Question

我是编码新手，需要回答这个问题。

这个问题是;

创建一个函数来接收一个字符串，该字符串将包含 Twitter 上的许多提及和主题标签。

   E.g. "So excited to start  @coding on Monday! #learntocode #codingbootcamp"

该函数应返回一个对象，描述找到的主题标签和提及的数量:

   { hashtags: 2, mentions: 1 }
 

我创建的代码是这样的；

function countHashtagsAndMentions(str) {
   let split = str.split(" ");
    let count = 0
    for (let i = 9; i < str.length; i++) {
        let hash = split.filter(hashtag => hashtag.match(/#/g))
        if (hash === 1) {
          count ++
         }
        let total = {
        hash = count,
      }
    return hash
   }
 }

我的代码正在针对此运行；

describe("countHashtagsAndMentions", () => {
  it("returns an object", () => {
    expect(typeof countHashtagsAndMentions("")).to.equal("object");
  });
  it("returns {hashtags: 0, mentions: 0} if it finds none", () => {
    expect(
      countHashtagsAndMentions(
        "hello this is a tweet guaranteed to get very little engagement"
      )
    ).to.eql({ hashtags: 0, mentions: 0 });
  });
  it("recognises no mentions", () => {
    expect(countHashtagsAndMentions("#yolo")).to.eql({
      hashtags: 1,
      mentions: 0
    });
  });
  it("recognises no hashtags", () => {
    expect(countHashtagsAndMentions("@yobo")).to.eql({
      hashtags: 0,
      mentions: 1
    });
  });
  it("finds multiple hashtags and mentions and returns that number", () => {
    expect(countHashtagsAndMentions("#yolo @bolo #golo")).to.eql({
      hashtags: 2,
      mentions: 1
    });
    expect(countHashtagsAndMentions("@boyo #goyo @loyo #zoyo")).to.eql({
      hashtags: 2,
      mentions: 2
    });
    expect(
      countHashtagsAndMentions(
        '"So excited to start at @northcoders on Monday! #learntocode #codingbootcamp"'
      )
    ).to.eql({ hashtags: 2, mentions: 1 });
  });
});

有没有人对如何使我的代码正常工作有任何建议？

Answer 1

一个简单的循环就可以做到。由于您使用的是 ES2015+ 语法，因此 for-of 可以很好地工作:

function countHashtagsAndMentions(str) {
  let hashtags = 0;
  let mentions = 0;
  for (const ch of str) {
    if (ch === "#") {
      ++hashtags;
    } else if (ch === "@") {
      ++mentions;
    }
  }
  return {hashtags, mentions};
}
let str = "So excited to start  @coding on Monday! #learntocode #codingbootcamp";
console.log(countHashtagsAndMentions(str));

这是可行的，因为字符串是 iterable在 ES2015+ 中。 for-of loop隐式使用字符串中的迭代器遍历其字符。所以在循环中，ch 是字符串中的每个字符。请注意，与 str.split() 不同，字符串迭代器不会将需要代理项对(如大多数表情符号)的字符的两半分开，这通常是您想要的。

这个:

for (const ch of str) {
    // ...
}

实际上等同于

let it = str[Symbol.iterator]();
let rec;
while (!(rec = it.next()).done) {
    const ch = rec.value;
    // ...
}

但没有 it 和 rec 变量。

---

或者，您可以使用带有正则表达式的 replace 来替换除您要计数的字符之外的所有字符。听起来它会更昂贵，但它是 JavaScript 引擎可以优化的东西:

function countHashtagsAndMentions(str) {
  return {
    hashtags: str.replace(/[^#]/g, "").length,
    mentions: str.replace(/[^@]/g, "").length
  };
}
let str = "So excited to start  @coding on Monday! #learntocode #codingbootcamp";
console.log(countHashtagsAndMentions(str));

您使用哪种可能部分取决于字符串的长度。 replace 选项很好而且很短，但确实会遍历字符串两次。