worker-search.ts

function createWorker(items: string[]) {
  const code = makeCode(JSON.stringify(items));

  const blob = new Blob(code, {
    type: 'text/javascript',
  });

  const blobUrl = URL.createObjectURL(blob);

  const worker = new Worker(blobUrl);

  return {
    worker,
    search(term: string) {
      return new Promise<{ distance: number; value: string }[]>((resolve) => {
        worker.postMessage(term);

        function listener(message: {
          data: { distance: number; value: string }[];
        }) {
          if (Array.isArray(message.data)) {
            worker.removeEventListener('message', listener);
            resolve(message.data);
          }
        }

        worker.addEventListener('message', listener);
      });
    },
  };
}

function makeCode(items: string) {
  const leven = `
// https://github.com/sindresorhus/leven
const array = [];
const charCodeCache = [];


const leven = (left, right) => {
	if (left === right) {
		return 0;
	}

	const swap = left;

	if (left.length > right.length) {
		left = right;
		right = swap;
	}
	let leftLength = left.length;
	let rightLength = right.length;
	while (leftLength > 0 && (left.charCodeAt(~-leftLength) === right.charCodeAt(~-rightLength))) {
		leftLength--;
		rightLength--;
	}
	let start = 0;
	while (start < leftLength && (left.charCodeAt(start) === right.charCodeAt(start))) {
		start++;
	}
	leftLength -= start;
	rightLength -= start;
	if (leftLength === 0) {
		return rightLength;
	}
	let bCharCode;
	let result;
	let temp;
	let temp2;
	let i = 0;
	let j = 0;

	while (i < leftLength) {
		charCodeCache[i] = left.charCodeAt(start + i);
		array[i] = ++i;
	}

	while (j < rightLength) {
		bCharCode = right.charCodeAt(start + j);
		temp = j++;
		result = j;

		for (i = 0; i < leftLength; i++) {
			temp2 = bCharCode === charCodeCache[i] ? temp : temp + 1;
			temp = array[i];
			result = array[i] = temp > result ? temp2 > result ? result + 1 : temp2 : temp2 > temp ? temp + 1 : temp2;
		}
	}

	return result;
};`;

  const code = `
${leven};

const cache = new Map();
function findCached(term, value){
  const key = \`\${term}##\${value}\`;
  if(cache.has(key)) return cache.get(key);

  term = term.toLowerCase();
  value = value.toLowerCase();

  const dist = (() => {
    const dist = Math.min(leven(term,value));

    if(term.length >=4) {
      if(value.startsWith(term)) return Math.min(dist, 1);
      if(value.includes(term)) return Math.min(dist, 1.5);
    }

    return dist;
  })();

  cache.set(key, dist);
  return dist;
}

const items = ${items};

function findClosestMatches(term) {
    return items.map(value => {
      return [
        { value, distance: findCached(term, value) },
        // { value, distance: findCached(term.slice(0,4), value.slice(0,4)) }
      ];
    })
    .flat()
    .sort((a, b) => a.distance - b.distance)
    .filter(el => el.distance < 5)
    .slice(0, 50);
}


self.onmessage = function (message) {
  const term = message.data;
  try {
    self.postMessage(findClosestMatches(term));
  } catch (e) {
    console.info(e);
  }
}`;

  return [code];
}