> ## Documentation Index
> Fetch the complete documentation index at: https://arizeai-433a7140.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# 05.14.2025: Experiments in the JS client

<Update label="05.14.2025">
  ## Experiments In The JS Client

  <Frame>
    <iframe src="https://cdn.iframe.ly/4vqTlUCW" width={1000} height={400} allowFullScreen />
  </Frame>

  You can now run Experiments using the Phoenix JS client! Use Experiments to test different iterations of your applications over a set of test cases, then evaluate the results.

  This release includes:

  * Native tracing of tasks and evaluators
  * Async concurrency queues
  * Support for any evaluator (including bring your own evals)

  ### Code Implementation

  ```javascript theme={null}
  import { createClient } from "@arizeai/phoenix-client";
  import {
    asEvaluator,
    runExperiment,
  } from "@arizeai/phoenix-client/experiments";
  import type { Example } from "@arizeai/phoenix-client/types/datasets";
  import { Factuality } from "autoevals";
  import OpenAI from "openai";

  const phoenix = createClient();
  const openai = new OpenAI();

  /** Your AI Task */
  const task = async (example: Example) => {
    const response = await openai.chat.completions.create({
      model: "gpt-4o",
      messages: [
        { role: "system", content: "You are a helpful assistant." },
        { role: "user", content: JSON.stringify(example.input, null, 2) },
      ],
    });
    return response.choices[0]?.message?.content ?? "No response";
  };

  await runExperiment({
    dataset: "dataset_id",
    experimentName: "experiment_name",
    client: phoenix,
    task,
    evaluators: [
      asEvaluator({
        name: "Factuality",
        kind: "LLM",
        evaluate: async (params) => {
          const result = await Factuality({
            output: JSON.stringify(params.output, null, 2),
            input: JSON.stringify(params.input, null, 2),
            expected: JSON.stringify(params.expected, null, 2),
          });
          return {
            score: result.score,
            label: result.name,
            explanation: (result.metadata?.rationale as string) ?? "",
            metadata: result.metadata ?? {},
          };
        },
      }),
    ],
  });
  ```
</Update>