JS How to create a function that count the number of hashtags

user_10806671 0
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numbers count loops javascript
3 Answers

A simple loop does it. Since you're using ES2015+ syntax, a for-of would work nicely:

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));

That works because strings are iterable in ES2015+. The for-of loop implicitly uses the iterator from the string to walk through its characters. So within the loop, ch is each character from the string. Note that unlike str.split(), a strings iterator doens't separately the two halves of a character that requires a surrogate pair (like most emojis), which is normally what you want.

This:

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

is effectively the same as

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

but without the it and rec variables.

Alternately, you could use replace with a regular expression to replace all characters other than the ones you want to count. It sounds like it would be more expensive, but it's something the JavaScript engine can optimize:

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));

Which you use probably depends in part on the length of the string. The replace option is nice and short, but does go through the string twice.

user_1572470

You could use an object for checking and counting.

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));

user_14476750

Use Array#reduce

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);

user_35890920
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