Yes, it is possible to check if a user was exposed to an experiment using the JavaScript SDK. However, it's important to note that the SDK methods will only show how users would be or have been allocated, not if they have actually been exposed to the experiment.
To get a list of users who have actually been exposed to an experiment, you can use the Daily Reports feature of the Statsig console API. This feature allows you to download lists of users that have been exposed to the experiment.
Additionally, you can navigate to the users page and type in a specific user ID. This will show the list of recent exposures. You can click on any of them, and it will show all the associated metadata, including the SDK type that was used for assignment.
For more detailed information, you can refer to the following documentation: Daily Reports | Statsig Docs.