I wanted to receive error notification when my ec2 instances CloudWatch metric passes a set threshold and as such was looking for a means to get notification sent to Slack, as a means to avoid the general noise in email notifications.
To this end I discovered "How To Set Up A Slack Channel To Be An AWS SNS Subscriber" which is easily adaptable via SNS itself.
Having tested the Node Lambda function, don't forget to ensure that you subscribe the Lambda function to the SNS topic. When done correctly, within AWS' console > SNS > Subscriptions you should see details of the lambda function specified with a Subscription ID and protocol as lambda.