See https://github.com/dddddddddzzzz/OpenHeart

worker.js

export default {
  async fetch(request, env) {
    if (request.method !== 'POST' && request.method !== 'GET') {
      return
    }

    else if (request.method == 'POST') {
      const url = new URL(request.url)
      const id = url.searchParams.get('id')
      const emoji = ensureEmoji(await request.text())

      if (!id || !emoji) return new Response('not ok', {status: 500})

      const key = `${id}:${emoji}`

      // https://developers.cloudflare.com/workers/runtime-apis/kv/
      const currentCount = Number(await(env.NAMESPACE.get(key)) || 0)
      await env.NAMESPACE.put(key, currentCount + 1)

      return new Response('ok')
    }

    else if (request.method == 'GET') {
      const url = new URL(request.url)
      const id = url.searchParams.get('id')
      const prefix = id + ":"

      const listResult = await env.NAMESPACE.list({ prefix: prefix })
      const keys = (listResult.keys || 0)

      const values = {}
      for (var key in keys) {
        const name = keys[key]["name"]
        const emoji = name.slice(prefix.length);
        const count = await env.NAMESPACE.get(name)
        values[emoji] = parseInt(count)
      }

      return Response.json(values, {
        headers: {
          "content-type": "application/json",
          "Access-Control-Allow-Origin": "https://YOURWEBSITE.COM",
          "Access-Control-Allow-Methods": "GET"
        }
      })
    }
  }
}

function ensureEmoji(emoji) {
  const segments = Array.from(new Intl.Segmenter({ granularity: 'character' }).segment(emoji.trim()))
  const parsedEmoji = segments.length > 0 ? segments[0].segment : null

  if (/\p{Emoji}/u.test(parsedEmoji)) return parsedEmoji
}