Anyone know Javascript and Sharepoint Online?

Scenario

Creating a new List item on a Sharepoint site - Before the Item is displayed and filled in, you first get some T&C's text and a small tick-box to show they have read the above text - once ticked then the rest of the list appears ready to be filled in.

Would this be best suited to a workflow or a custom action - if so, how would be best to go about this?

Thanks in advance.

CrazyAl