How can I count the number of times different terms occur in a string string with JavaScript?

Question

I have a list of 20 phrases that I want to count in an article.

Currently, I'm doing

      let counts = phrases.map((phrase, idx) => {
        phrase.usage = (articleBody.match(new RegExp(phrase.phrase, 'gi')) || []).length
        return phrase
      })

This requires me to do an expensive search each time. Is there some way to do it faster or all at once?

Answer 1

You can use String.prototype.matchAll

const str = ['ocurrence 1, and..', 'ocurrence 2, and..', 'other phrases'];

const array = [...str.join ` `.matchAll(new RegExp('ocurrence', 'gi'))];

console.log(array.length); // 2

Edit: counting occurrences in one string;

const articleBody = 'ocurrence 1, and.. ocurrence 2, and... etc';
const array = [...articleBody.matchAll(new RegExp('ocurrence', 'gi'))];

console.log(array.length) // 2;

Edit 2:

Using a service worker

I created a text of 3000 words ("Lorem ipsum" generator).

main.js

if ("serviceWorker" in navigator) {
         document.addEventListener("DOMContentLoaded", function () {
         const phrases = [
            { text: "Lorem ipsum" },
            { text: "elementum mattis" },
          ];
          phrases.map((phrase, index) => {
            const phraseWorker = new Worker("phrase-match-sw.js");

            phraseWorker.onmessage = function (oEvent) {
              const { text, match } = oEvent.data;
              phrases[index] = { text, match };
            };

            phraseWorker.postMessage({
              article:
                "Lorem ipsum dolor sit amet consectetur adipiscing elit sapien orci, ligula leo consequat mus tellus elementum mattis lacus maecenas curabitur, ",
              phrase,
            });
          });
        });
      }

phrase-match-sw.js

onmessage = function (event) {
  const { article, phrase } = event.data;
  phrase.match = [...article.matchAll(new RegExp(phrase.text,"gi"))].length;
  postMessage(phrase);
};