Getting started in a browser script - Amazon SDK for JavaScript
Services or capabilities described in Amazon Web Services documentation might vary by Region. To see the differences applicable to the China Regions, see Getting Started with Amazon Web Services in China (PDF).

The Amazon SDK for JavaScript V3 API Reference Guide describes in detail all the API operations for the Amazon SDK for JavaScript version 3 (V3).

Getting started in a browser script

This section walks you through an example that demonstrates how to run version 3 (V3) of the SDK for JavaScript in the browser.


Running V3 in the browser is slightly different from version 2 (V2). For more information, see Using browsers in V3.

For other examples of using (V3) of the SDK for JavaScript with the Node.js in the browser, see:

JavaScript code example that applies to browser execution

This browser script example shows you:

  • How to access Amazon services from a browser script using Amazon Cognito Identity.

  • How to turn text into synthesized speech using Amazon Polly.

  • How to use a presigner object to create a presigned URL.

The Scenario

Amazon Polly is a cloud service that converts text into lifelike speech. You can use Amazon Polly to develop applications that increase engagement and accessibility. Amazon Polly supports multiple languages and includes a variety of lifelike voices. For more information about Amazon Polly, see the Amazon Polly Developer Guide.

This example shows you how to set up and run a browser script that takes text, sends that text to Amazon Polly, and returns the URL of the synthesized audio of the text for you to play. The browser script uses an Amazon Cognito Identity pool to provide credentials needed to access Amazon services. The example demonstrates the basic patterns for loading and using the SDK for JavaScript in browser scripts.


You must run this example in a browser that supports HTML 5 audio to playback the synthesized speech.

                        Illustration of how a browser script interacts with Amazon Cognito Identity and Amazon Polly services

The browser script uses the SDK for JavaScript to synthesize text by using the following APIs:

Step 1: Create an Amazon Cognito Identity Pool

In this exercise, you create and use an Amazon Cognito Identity pool to provide unauthenticated access to your browser script for the Amazon Polly service. Creating an identity pool also creates two Amazon Identity and Access Management (IAM) roles, one to support users authenticated by an identity provider and the other to support unauthenticated guest users.

In this exercise, we will only work with the unauthenticated user role to keep the task focused. You can integrate support for an identity provider and authenticated users later.

To create an Amazon Cognito Identity pool
  1. Sign in to the Amazon Web Services Management Console and open the Amazon Cognito console at Amazon Web Services Console.

  2. Choose Manage Identity Pools on the console opening page.

  3. On the next page, choose Create new identity pool.


    If there are no other identity pools, the Amazon Cognito console will skip this page and open the next page instead.

  4. In the Getting started wizard, type a name for your identity pool in Identity pool name.

  5. Choose Enable access to unauthenticated identities.

  6. Choose Create Pool.

  7. On the next page, choose View Details to see the names of the two IAM roles created for your identity pool. Make a note of the name of the role for unauthenticated identities. You need this name to add the required policy for Amazon Polly.

  8. Choose Allow.

  9. On the Sample code page, select the Platform of JavaScript. Then, copy or write down the identity pool ID and the Region. You need these values to replace REGION and IDENTITY_POOL_ID in your browser script.

After you create your Amazon Cognito identity pool, you're ready to add permissions for Amazon Polly that are needed by your browser script.

Step 2: Add a Policy to the Created IAM Role

To enable browser script access to Amazon Polly for speech synthesis, use the unauthenticated IAM role created for your Amazon Cognito identity pool. This requires you to add an IAM policy to the role. For more information about IAM roles, see Creating a Role to Delegate Permissions to an Amazon Service in the IAM User Guide.

To add an Amazon Polly policy to the IAM role associated with unauthenticated users
  1. Sign in to the Amazon Web Services Management Console and open the IAM console at

  2. In the navigation panel on the left of the page, choose Roles.

  3. In the list of IAM roles, click the link for the unauthenticated identities role previously created by Amazon Cognito.

  4. In the Summary page for this role, choose Attach policies.

  5. In the Attach Permissions page for this role, find and then select the check box for AmazonPollyFullAccess.


    You can use this process to enable access to any Amazon service.

  6. Choose Attach policy.

After you create your Amazon Cognito identity pool and add permissions for Amazon Polly to your IAM role for unauthenticated users, you are ready to build the webpage and browser script.

Step 3: Create a project environment

Set up the project environment to run these Node TypeScript examples, and install the required Amazon SDK for JavaScript and third-party modules. Follow the instructions on GitHub.

Step 4: Create the HTML Page

The sample app consists of a single HTML page that contains the user interface, and a JavaScript file that contains the required JavaScript. To begin, create an HTML document and copy the following contents into it. The page includes an input field and button, an <audio> element to play the synthesized speech, and a <p> element to display messages. (Note that the full example is shown at the bottom of this page.)

The <script> element adds the main.js file, which contains all the required JavaScript for the example.

You use webpack to create the main.js file, as described in Step 5: Write the JavaScript.

For more information about the <audio> element, see audio.

The full HTML page is available here on GitHub.

Save the HTML file, naming it polly.html. After you have created the user interface for the application, you're ready to add the browser script code that runs the application.

To use V3 of the Amazon SDK for JavaScript in the browser, you require Webpack to bundle the JavaScript modules and functions, which you installed in the Step 3: Create a project environment.

Step 5: Write the JavaScript

Create a file named polly.js, and paste the code below into it. The full JavaScript page is available here on GitHub. The code first imports the required Amazon SDK clients and commands. Then it creates the Polly service client object, specifying the credentials for the SDK. To synthesize speech with Amazon Polly, it provides a variety of parameters including the sound format of the output, the sampling rate, the ID of the voice to use, and the text to play back. When you initially create the parameters, set the Text: parameter to an empty string; the Text: parameter will be set to the value you retrieve from the <input> element in the webpage.

Next, it creates a function named speakText() that is be invoked as an event handler by the button. Amazon Polly returns synthesized speech as an audio stream. The easiest way to play that audio in a browser is to have Amazon Polly make the audio available at a presigned URL you can then set as the src attribute of the <audio> element in the webpage.

Next it creates the Presigner object you'll use to create the presigned URL from which the synthesized speech audio can be retrieved. You must pass the speech parameters that you defined as well as the Polly service object that you created to the Polly.Presigner constructor.

After it creates the presigner object, it calls the getSynthesizeSpeechUrl method of that object, passing the speech parameters. If successful, this method returns the URL of the synthesized speech, which the code then assign to the <audio> element for playback.

Finally, from your project folder containing polly.js run the following at the command prompt to bundle the JavaScript for this example in a file named main.js:

webpack --entry polly.js --mode development --target web --devtool false -o main.js

For information about installing webpack, see Bundling applications with webpack.

import { CognitoIdentityClient } from "@aws-sdk/client-cognito-identity"; import { fromCognitoIdentityPool, } from "@aws-sdk/credential-provider-cognito-identity"; import { Polly } from "@aws-sdk/client-polly"; import { getSynthesizeSpeechUrl } from "@aws-sdk/polly-request-presigner"; // Create the Polly service client, assigning your credentials const client = new Polly({ region: "REGION", credentials: fromCognitoIdentityPool({ client: new CognitoIdentityClient({ region: "REGION" }), identityPoolId: "IDENTITY_POOL_ID" // IDENTITY_POOL_ID }), }); // Set the parameters const speechParams = { OutputFormat: "OUTPUT_FORMAT", // For example, 'mp3' SampleRate: "SAMPLE_RATE", // For example, '16000 Text: "", // The 'speakText' function supplies this value TextType: "TEXT_TYPE", // For example, "text" VoiceId: "POLLY_VOICE" // For example, "Matthew" }; const speakText = async () => { // Update the Text parameter with the text entered by the user speechParams.Text = document.getElementById("textEntry").value; try{ let url = await getSynthesizeSpeechUrl({ client, params: speechParams }); console.log(url); // Load the URL of the voice recording into the browser document.getElementById('audioSource').src = url; document.getElementById('audioPlayback').load(); document.getElementById('result').innerHTML = "Speech ready to play."; } catch (err) { console.log("Error", err); document.getElementById('result').innerHTML = err; } }; // Expose the function to the browser window.speakText = speakText;

Step 6: Run the Example

To run the example app, load polly.html into a web browser. The app should look similar to the following.

                        Web application browser interface

Enter a phrase you want turned to speech in the input box, then choose Synthesize. When the audio is ready to play, a message appears. Use the audio player controls to hear the synthesized speech.

Possible Enhancements

Here are variations on this application you can use to further explore using the SDK for JavaScript in a browser script.

  • Experiment with other sound output formats.

  • Add the option to select any of the various voices provided by Amazon Polly.

  • Integrate an identity provider like Facebook or Amazon to use with the authenticated IAM role.