TypeScript Streaming

~10 min · typescript, streaming, for-await

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generateContentStream returns an async iterable

Same shape as the Python async surface. generateContentStream returns an async iterable; consume it with for await ... of.

Same chunk shape

Each chunk is a partial GenerateContentResponse. chunk.text for the slice; chunk.usageMetadata on the final chunk only.

Streaming chat works the same way

chat.sendMessageStream mirrors the streaming non-chat call.

Code

Stream once·typescript

import { GoogleGenAI } from '@google/genai';

const ai = new GoogleGenAI({});

const stream = await ai.models.generateContentStream({
  model: 'gemini-2.5-flash',
  contents: 'Explain async iterators in 3 sentences.',
});

for await (const chunk of stream) {
  if (chunk.text) {
    process.stdout.write(chunk.text);
  }
}

Stream with usage capture·typescript

let finalUsage;
let fullText = '';

const stream = await ai.models.generateContentStream({
  model: 'gemini-2.5-flash',
  contents: 'Write a 200-word story.',
});

for await (const chunk of stream) {
  if (chunk.text) {
    fullText += chunk.text;
    process.stdout.write(chunk.text);
  }
  if (chunk.usageMetadata) {
    finalUsage = chunk.usageMetadata;
  }
}
console.log(`\n\n[total tokens: ${finalUsage?.totalTokenCount}]`);

Streaming chat·typescript

const chat = ai.chats.create({ model: 'gemini-2.5-flash' });

const stream = await chat.sendMessageStream({ message: 'Hi!' });
for await (const chunk of stream) {
  if (chunk.text) process.stdout.write(chunk.text);
}

External links

Exercise

Write a Node script stream.mjs that takes a prompt as argv and streams Flash to stdout. Add an AbortController with a 30-second timeout that cancels the stream cleanly. Confirm the output stops mid-flight when you ctrl-C, without leaving an open socket (check lsof -i :443 after).