If you need public data from multiple cryptocurrency exchanges but don't want to deal with weird differences in exchange APIs, Blocktap[1] is a free GraphQL API (that I assisted in developing). We also open sourced our web socket data collection tool CCXWS[2]. It's a single, consistent Javascript API for most major exchanges.

[1] https://www.blocktap.io/

[2] https://github.com/altangent/ccxws