If you've designed your client-side javascript (or swift or whatever it is) properly, you've abstracted out the API calls to say, AWS Lambda, and wrapped them such that the implementation is not tightly coupled to the calling code. Eg you write a generic Storage class and call Storage.Save, which wraps whatever API you use to save stuff, be it Lambda or otherwise. Change vendor and you just change your Storage class's implementation without needing to alter client functions..
If you've designed your client-side javascript (or swift or whatever it is) properly, you've abstracted out the API calls to say, AWS Lambda, and wrapped them such that the implementation is not tightly coupled to the calling code. Eg you write a generic Storage class and call Storage.Save, which wraps whatever API you use to save stuff, be it Lambda or otherwise. Change vendor and you just change your Storage class's implementation without needing to alter client functions..