Built-in AI Task APIs Polyfills

This package provides browser polyfills for the Built-in AI Task APIs, specifically:

• Summarizer API
• Writer API
• Rewriter API
• Language Detector API
• Translator API
• Classifier API

These polyfills are backed by the prompt-api-polyfill, which is automatically loaded if window.LanguageModel is not detected. This means they support the same dynamic backends.

When loaded in the browser, they define globals:

window.Summarizer;
window.Writer;
window.Rewriter;
window.LanguageDetector;
window.Translator;
window.Classifier;

so you can use these Task APIs even in environments where they are not yet natively available.

Installation

Install from npm:

npm install built-in-ai-task-apis-polyfills

Quick start

Recommended Loading Strategy

To ensure your app uses the native implementation when available, use a defensive dynamic import strategy:

<script type="module">
  import config from './.env.json' with { type: 'json' };

  // Example: Use Gemini backend
  window.GEMINI_CONFIG = config;

  // Load polyfills only if not natively supported
  const polyfills = [];
  if (!('Summarizer' in window)) {
    polyfills.push(import('built-in-ai-task-apis-polyfills/summarizer'));
  }
  if (!('Writer' in window)) {
    polyfills.push(import('built-in-ai-task-apis-polyfills/writer'));
  }
  if (!('Rewriter' in window)) {
    polyfills.push(import('built-in-ai-task-apis-polyfills/rewriter'));
  }
  if (!('LanguageDetector' in window)) {
    polyfills.push(import('built-in-ai-task-apis-polyfills/language-detector'));
  }
  if (!('Translator' in window)) {
    polyfills.push(import('built-in-ai-task-apis-polyfills/translator'));
  }
  if (!('Classifier' in window)) {
    polyfills.push(import('built-in-ai-task-apis-polyfills/classifier'));
  }
  await Promise.all(polyfills);

  // Now you can use the APIs
  if ((await Summarizer.availability()) === 'available') {
    const summarizer = await Summarizer.create();
    const summary = await summarizer.summarize('Long text to summarize...');
    console.log(summary);
  }
</script>

API Usage Examples

Summarizer API

const summarizer = await Summarizer.create({
  type: 'key-points',
  format: 'markdown',
  length: 'short',
});

const result = await summarizer.summarize(text);
// or streaming
const stream = summarizer.summarizeStreaming(text);
for await (const chunk of stream) {
  console.log(chunk);
}

Writer API

const writer = await Writer.create({
  tone: 'professional',
  format: 'plain-text',
});

const result = await writer.write('Draft of an email to my boss');

Rewriter API

const rewriter = await Rewriter.create({
  tone: 'casual',
});

const result = await rewriter.rewrite('I am writing to inform you that...');

Language Detector API

const detector = await LanguageDetector.create();
const results = await detector.detect('C'est la vie');

for (const { detectedLanguage, confidence } of results) {
  console.log(`${detectedLanguage} (${(confidence * 100).toFixed(1)}%)`);
}

Translator API

const translator = await Translator.create({
  sourceLanguage: 'en',
  targetLanguage: 'fr',
});

const result = await translator.translate('Hello world');

Classifier API

const classifier = await Classifier.create();
const results = await classifier.classify('A story about a cat');

for (const { id, confidence } of results) {
  console.log(`${id} (${(confidence * 100).toFixed(1)}%)`);
}

Configuration

Configuring .env.json

This repo ships with a dot_env.json template. Copy it to .env.json and fill in your credentials:

cp dot_env.json .env.json

The polyfill will look for these configurations on the window object. Adjust your loading logic to pass the JSON content to the appropriate global (e.g., window.GEMINI_CONFIG).

API surface

Once the polyfills are loaded, you can use them as described in the official documentation:

• Summarizer API
• Writer API
• Rewriter API
• Language Detector API
• Translator API

For complete examples, see:

• demo_summarizer.html
• demo_writer.html
• demo_rewriter.html
• demo_language_detector.html
• demo_translator.html
• demo_classifier.html

Running the demos locally

1. Install dependencies:

   npm install

2. Copy and fill in your config:

   cp dot_env.json .env.json

3. Start the server:

   npm start

Testing

The project includes a comprehensive test suite based on Web Platform Tests (WPT).

npm run test:wpt

License

Apache 2.0