How to access the Vkontakte API using openapi or javascript SDK and what is the difference between them?

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I am making a site that will open in an iframe inside Vkontakte and as a separate site. The documentation says that to call methods from iframe applications, you need to use the javascript sdk, which does not work outside the iframe. In this case, the use of both sdk and openapi can lead to a conflict.
It turns out that I need to use different libraries depending on whether it is an iframe or a website?
How to be?