How to get API GW Socket URL outside of lambda handler?

[entest-hai]

This current example [api-websocket-lambda-dynamodb](https://github.com/aws-samples/aws-cdk-examples/blob/master/typescript/api-websocket-lambda-dynamodb/sendmessage/app.js) get the endpointUrl of a deployed socket api as below.

 const apigwManagementApi = new AWS.ApiGatewayManagementApi({
    apiVersion: '2018-11-29',
    endpoint: event.requestContext.domainName + '/' + event.requestContext.stage
  });

However, this is inside a handler lambda. It is better to do this outside (from very beginning). I am considering query the endpointUrl by boto3 ... but not nice. Does anyone know how to get the endpointUrl?