Clarify how TTL works (i.e. only when the user ever revisits my website)

[ThomasLandauer]

The term "TTL" (time-to-live) creates the impression that items will actually get deleted after that time. But this is not always the case: If somebody visits my websites, and I save something into the user's LocalStorage, and the user never returns to my website, the stuff stays in the user's LocalStorage forever.

I think you should clarify this in README.

[niketpathak]

Thank you for your comment @ThomasLandauer. Localstorage is not built for this (I haven't documented it because its already there in the official documentation of LocalStorage). If someone else was able to read or delete your data using this library, that would be bad since its a breach of security/privacy and the localstorage API doesn't allow that.
To accomplish what you want, you can use something else that supports expiry time by design. for example: cookies .

Hope that helps :)