The [AWS SDK for JavaScript V3 API Reference Guide](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/) describes in detail all the API operations for the AWS SDK for JavaScript version 3 (V3). 

# Notes on specific service clients
<a name="migrate-service-client-notes"></a>

## AWS Lambda
<a name="aws-lambda-notes"></a>

 Lambda invocations response type differs in v2 and v3. 

```
// v2
import { Lambda } from "@aws-sdk/client-lambda";
import AWS from "aws-sdk";

const lambda = new AWS.Lambda({ {{REGION}} });
const invoke = await lambda.invoke({
  FunctionName: "echo",
  Payload: JSON.stringify({ message: "hello" }),
}).promise();

// in v2, Lambda::invoke::Payload is automatically converted to string via a
// specific code customization.
const payloadIsString = typeof invoke.Payload === "string";
console.log("Invoke response payload type is string:", payloadIsString);

const payloadObject = JSON.parse(invoke.Payload);
console.log("Invoke response object", payloadObject);
```

```
// v3
const lambda = new Lambda({ {{REGION}} });
const invoke = await lambda.invoke({
  FunctionName: "echo",
  Payload: JSON.stringify({ message: "hello" }),
});

// in v3, Lambda::invoke::Payload is not automatically converted to a string.
// This is to reduce the number of customizations that create inconsistent behaviors.
const payloadIsByteArray = invoke.Payload instanceof Uint8Array;
console.log("Invoke response payload type is Uint8Array:", payloadIsByteArray);

// To maintain the old functionality, only one additional method call is needed:
// v3 adds a method to the Uint8Array called transformToString.
const payloadObject = JSON.parse(invoke.Payload.transformToString());
console.log("Invoke response object", payloadObject);
```

## Amazon SQS
<a name="amazon-sqs-notes"></a>

### MD5 Checksum
<a name="md5-checksum"></a>

 To skip computation of MD5 checksums of message bodies, set `md5` to *false* on the configuration object. Otherwise, the SDK by default will calculate the checksum for sending messages, as well as validating the checksum for retrieved messages.

```
// Example: Skip MD5 checksum in Amazon SQS
import { SQS } from "@aws-sdk/client-sqs";

new SQS({
  md5: false // note: only available in v3.547.0 and higher
});
```

When using a custom `QueueUrl` in Amazon SQS operations that have this as an input parameter, in v2 it was possible to supply a custom `QueueUrl` which would override the Amazon SQS Client's default endpoint. 

### Multi-region messages
<a name="multi-region-messages"></a>

 You should use one client per region in v3. The AWS region is meant to be initialized at the client level and not changed between requests. 

```
import { SQS } from "@aws-sdk/client-sqs";

const sqsClients = {
  "us-east-1": new SQS({ region: "us-east-1" }),
  "us-west-2": new SQS({ region: "us-west-2" }),
};

const queues = [
  { region: "us-east-1", url: "https://sqs.us-east-1.amazonaws.com/{AWS_ACCOUNT}/MyQueue" },
  { region: "us-west-2", url: "https://sqs.us-west-2.amazonaws.com/{AWS_ACCOUNT}/MyOtherQueue" },
];

for (const { region, url } of queues) {
  const params = {
    MessageBody: "Hello",
    QueueUrl: url,
  };
  await sqsClients[region].sendMessage(params);
}
```

### Custom endpoint
<a name="custom-endpoint"></a>

 In v3, when using a custom endpoint, i.e. one that differs from the default public Amazon SQS endpoints, you should always set the endpoint on the Amazon SQS Client as well as the ` QueueUrl` field. 

```
import { SQS } from "@aws-sdk/client-sqs";

const sqs = new SQS({
  // client endpoint should be specified in v3 when not the default public SQS endpoint for your region.
  // This is required for versions <= v3.506.0
  // This is optional but recommended for versions >= v3.507.0 (a warning will be emitted)
  endpoint: "https://my-custom-endpoint:8000/",
});

await sqs.sendMessage({
  QueueUrl: "https://my-custom-endpoint:8000/1234567/MyQueue",
  Message: "hello",
});
```

 If you are not using a custom endpoint, then you do not need to set `endpoint` on the client.

```
import { SQS } from "@aws-sdk/client-sqs";

const sqs = new SQS({
  region: "us-west-2",
});

await sqs.sendMessage({
  QueueUrl: "https://sqs.us-west-2.amazonaws.com/1234567/MyQueue",
  Message: "hello",
});
```