Safe/secure way to load plugins into web app

I have a web app that accepts JS plugins. That is, JavaScript code that someone else wrote that the user wants to load into my app.

Currently I am using eval() to evaluate their JS code into the runtime, but I know thats not secure. Is there a better method than eval() for doing this?

To be clear, the user is pointing me to a dry text file, and that JS in the file needs to come to life somehow.

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