JS如何创建一个计算标签数量的函数

Question

我是编码新手，有人问我这个问题。

这个问题是；

创建一个函数，该函数接收一个字符串，该字符串将包含Twitter上的许多提及和标签。

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

函数应该返回一个对象，描述找到的标签和提及的数量：

{ 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
}
}

我的代码是针对这个运行的；

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 });
});
});

有人对如何使我的代码工作有任何建议吗？

Answer 1

一个简单的循环就可以做到这一点。由于您使用的是ES2015+语法，for-of会很好地工作：

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));

这是因为字符串在ES2015+中是可迭代的。for-of循环隐式地使用字符串中的迭代器遍历其字符。因此，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对的字符的两半分开(就像大多数表情符号一样)，这通常是您想要的。

此：

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

实际上与相同

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

但没有CCD_ 5和CCD_。

---

或者，可以将replace与正则表达式一起使用，以替换除要计数的字符之外的所有字符。听起来它会更贵，但这是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));

你使用的可能在一定程度上取决于字符串的长度。replace选项很好，很短，但确实会遍历字符串两次。

Answer 2

您可以使用对象进行检查和计数。

function countHashtagsAndMentions(str) {
var result = { '#': 0, '@': 0 },
i;
for (i = 0; i < str.length; i++) {
if (str[i] in result) ++result[str[i]];
}
return result;
}
var str = "So excited to start  @coding on Monday! #learntocode #codingbootcamp";
console.log(countHashtagsAndMentions(str));

Answer 3

使用数组#减少

const message = "So excited to start @coding on Monday! #learntocode #codingbootcamp"
const res = message.split("").reduce((acc,cur)=>{

if('#@'.includes(cur)){
const key = cur === '#' ? 'hashtags' : 'mentions';
acc[key] = acc[key] + 1;
}

return acc;
}, {mentions: 0, hashtags: 0})
console.log(res);