[Svelte] Reload image on fail to fetch

reloadImgOnFail.js

export function reloadImgOnFail(img, opts = {}) {
  opts = ensureOpts(opts)

  let retryCount = 0

  function handleError() {
    if (retryCount >= opts.maxRetryCount) {
      if (opts.fallbackSrc && img.src !== opts.fallbackSrc) {
        img.src = opts.fallbackSrc
      }
    } else {
      setTimeout(() => (img.src = img.src), opts.getTimeout(retryCount++))
    }
  }

  function ensureOpts(o) {
    return {
      getTimeout: o.getTimeout ?? ((n) => n * n + 1),
      maxRetryCount: o.maxRetryCount ?? 3,
      fallbackSrc: o.fallbackSrc
    }
  }

  img.addEventListener('error', handleError)

  return {
    update(newOpts = {}) {
      opts = ensureOpts(newOpts)
    },
    destroy() {
      img.removeEventListener('error', handleError)
    }
  }
}