Ah yeah. The only documentation we reference that I can find is virtual-dom/virtual-hyperscript/README.md at master · Matt-Esch/virtual-dom · GitHub and it’s sort of hidden in our codebase as a comment 
Even with that I couldn’t find the answer you are looking for there. In any case, there is a topic here on Meta that does have the solution:
So based on the code you provided, it should work if you change it to the following:
h("script", { src: "http://localhost:5000/pass.js", attributes: { "data-space": "123" } }),