An example of OpenAI API and ReadableStream with GPT 3 in SvelteKit

From this GitHub snippet:

async function OpenAITextStream(search: string) {
  const payload: OpenAITextPayload = {
    model: "text-davinci-003",
    prompt: search,
    temperature: 0,
    max_tokens: 2048,
    frequency_penalty: 0.0,
    stream: true,
    presence_penalty: 0.0,
    n: 1,
  };

  const encoder = new TextEncoder();
  const decoder = new TextDecoder();

  let counter = 0;

  const res = await fetch("https://api.openai.com/v1/completions", {
    headers: {
      "Content-Type": "application/json",
      Authorization: `Bearer ${key}`,
    },
    method: "POST",
    body: JSON.stringify(payload),
  });

  const stream = new ReadableStream({
    async start(controller) {
      // eslint-disable-next-line @typescript-eslint/no-explicit-any
      function onParse(event: ParseEvent) {
        if (event.type === "event") {
          const data = event.data;
          // https://beta.openai.com/docs/api-reference/completions/create#completions/create-stream
          if (data === "[DONE]") {
            controller.close();
            return;
          }
          try {
            const json = JSON.parse(data);
            const text = json.choices[0].text;

            if (counter < 2 && (text.match(/\n/) || []).length) {
              // this is a prefix character (i.e., "\n\n"), do nothing
              return;
            }
            const queue = encoder.encode(text);
            controller.enqueue(queue);
            counter++;
          } catch (e) {
            controller.error(e);
          }
        }
      }

      // stream response (SSE) from OpenAI may be fragmented into multiple chunks
      // this ensures we properly read chunks and invoke an event for each SSE event stream
      const parser = createParser(onParse);
      // https://web.dev/streams/#asynchronous-iteration
      // eslint-disable-next-line @typescript-eslint/no-explicit-any
      for await (const chunk of res.body as any) {
        parser.feed(decoder.decode(chunk));
      }
    },
  });
  return stream;
}