value.forEach((str) => {
  encodedValue = shouldEncode ? encodeURIComponent(str) : str;
  item += `${key}=${encodedValue}&`;
});
// last character will always be "&" so slice it off
item.slice(0, -1);  // ❌ Result not assigned!

return output.substr(1);  // ❌ substr is deprecated

buildUrlParams({ tags: ['javascript', 'typescript'], key: 'value' })
// Should return: "tags=javascript&tags=typescript&key=value"

buildUrlParams({ tags: ['javascript', 'typescript'], key: 'value' })
// Returns: "tags=javascript&tags=typescript&&key=value"  // Note the &&

item = item.slice(0, -1);

return output.substring(1);