How do I check if a vector exists in the Supabase vector database?

Question

const data = await req.json();
  const { url, prompt } = data;

  const model = new ChatOpenAI({ modelName: "gpt-3.5-turbo" });
  const loader = new CheerioWebBaseLoader(url);

  const docs = await loader.load();

  const splitter = RecursiveCharacterTextSplitter.fromLanguage("html");
  const transformer = new HtmlToTextTransformer({
    removeLineBreaks: true,
    removeMultipleSpaces: true,
  });

  const sequence = splitter.pipe(transformer);

  const newDocuments = await sequence.invoke(docs);

  const client = createClient(
    process.env.SUPABASE_URL,
    process.env.SUPABASE_API_KEY
  );
  const vectorStore = await SupabaseVectorStore.fromDocuments(
    newDocuments,
    new OpenAIEmbeddings(),
    {
      client,
      tableName: "documents",
      queryName: "match_documents",
    }
  );

I create a document from a URL and save it to the vector database, but it is saving it to the database even if the same URL is sent each time. How can I control this?