I'm a beginner in marketing cloud and Journey Builder dev, so sorry if the question seems stupid but I'm struggling on a little problem, I would like to know if in a custom activity, running with NodeJs you could create a Data Extension (and put contacts in it) in marketing cloud because I found this doc : https://developer.salesforce.com/docs/atlas.en-us.noversion.mc-apis.meta/mc-apis/creating_a_data_extension_using_web_service_api.htm , there are different ways to create a data extension (php,.NET,...) but not in NodeJS. Maybe around the SOAP API but I don't know what to do with it. Thanks!
Custom activity would not have direct access to the Marketing Cloud, since it will be hosted outside of it.
However you can create data extension via API, by implementing SOAP API call manually or by using Node SDK