Added Streaming.ipynb notebook for JavaScript

[Aarchi-07]

• Converted the original Python notebook into JavaScript.
• Added proper structure and formatting for better readability.
• Verified code compatibility and tested basic functionality.

[gemini-code-assist]

Summary of Changes

Hello @Aarchi-07, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces a new quickstart guide for the Gemini API, specifically demonstrating streaming capabilities in JavaScript. It serves as a direct conversion from an existing Python notebook, ensuring developers can easily understand and implement streaming responses using the JavaScript SDK. The notebook includes examples for basic streaming and asynchronous handling, along with setup instructions for the API key.

Highlights

• New JavaScript Streaming Quickstart: A new notebook, 'Streaming Quickstart.txt', has been added to demonstrate streaming capabilities of the Gemini API using the JavaScript SDK.
• Python to JavaScript Conversion: The content of this new quickstart guide is a direct conversion from an existing Python notebook, making it easier for JavaScript developers to adopt streaming.
• Asynchronous Streaming Examples: The notebook includes practical examples showcasing how to use generateContentStream and handle streaming responses asynchronously, ensuring applications remain responsive.

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[gemini-code-assist]

Code Review

This pull request adds a JavaScript quickstart for streaming, which is a great addition. I have a few general suggestions:

• The file is named Streaming Quickstart.txt. To be consistent with other files in the quickstarts-js directory, it should probably be a JavaScript file, for example Streaming.js or Streaming_Quickstart.js.
• The repository's style guide mentions that new notebooks should be added to the corresponding README.md file. This new quickstart is missing from quickstarts-js/README.md.

I've also added a couple of specific comments to improve the code quality by declaring variables properly and fixing a potential bug where undefined could be printed to the console.

[gemini-code-assist]

If a streamed chunk does not have a text property, console.log(chunk.text) will print undefined to the console. To make the code more robust, you should check for the existence of chunk.text before logging it. A short-circuit conditional is a concise way to do this, and this pattern is used correctly in the asynchronous example later in the file.

  chunk.text && console.log(chunk.text);

[gemini-code-assist]

In JavaScript, it's a best practice to declare all variables with const, let, or var to define their scope and prevent them from becoming implicit global variables. This improves code predictability and maintainability.

I suggest using const for these variables since they are not reassigned. I've also used object destructuring to import GoogleGenAI, which is a more modern and concise syntax.

const module = await import("https://esm.sh/@google/genai@1.4.0");
const { GoogleGenAI } = module;
const ai = new GoogleGenAI({ apiKey: process.env.GEMINI_API_KEY });

const MODEL_ID = "gemini-2.5-flash" // ["gemini-2.5-flash-lite", "gemini-2.5-flash", "gemini-2.5-pro"]

[gemini-code-assist]

To avoid creating an implicit global variable, it's best to declare response using const since it's not reassigned.

const response = await ai.models.generateContentStream({
  model: MODEL_ID,
  contents: "Tell me a story in 300 words.",
});