All of the SDKs for Azure services are mostly autogenerated from the Swagger files. In the case of the .NET SDK, our team adds additional classes for exceptions.
I checked with the SDK team for Javascript and they also confirmed the same.
The OpenAPI (swagger file) for Media Services does not define exception types, it only defines the different status codes and error responses.
You can see that by looking at our Open API documents for the latest version here - https://github.com/Azure/azure-rest-api-specs/tree/master/specification/mediaservices/resource-manager/Microsoft.Media/stable/2020-05-01
In JS, it is common to not have a different error class for different scenarios. In the auto generated JS SDKs, the errors thrown by the service or any serialization errors use the RestError class.
The SDK team for javascript could probably do a better job of documenting the usage of that though- please file an issue on them here · Azure/autorest.typescript (github.com) ?