Q:

How do I access a POST parameter in Node js AWS Lambda with API Gateway integration? 

I know how to access GET string variables in a Node js Lambda that is integrated with API Gateway with:
 event["queryStringParameters"]["variable_name"]

What is the equivalent for accessing POST variables? 

A:

Use the following
if (event.body ! == null && event.body ! == undefined) {
        let body = JSON.parse(event.body) 
        //your code
}

AWS Documentation

