sls deploy function command deploys an individual function without AWS CloudFormation. This command simply swaps out the zip file that your CloudFormation stack is pointing toward. This is a much faster way of deploying changes in code.
serverless deploy function -f functionName
Note: This command now deploys both function configuration and code by default. Just as before, this puts your function in an inconsistent state that is out of sync with your CloudFormation stack. Use this for faster development cycles and not production deployments
-fThe name of the function which should be deployed
-sThe stage in your service that you want to deploy to.
-rThe region in that stage that you want to deploy to.
-uPushes ONLY Lambda-level configuration changes e.g. handler, timeout or memorySize
serverless deploy function --function helloWorld
serverless deploy function --function helloWorld \ --stage dev \ --region us-east-1
serverless deploy function --function helloWorld --update-config