Hello @Wu_Nokiri,
Thank you for giving the insight to this, @Steve_White.
We would like to provide more detail if you’re creating the keyboard as a new project (a keyboard package just for the iPhone).
There is no need for JavaScript knowledge to get started with keyboard development using Keyman Developer. Feel free to read more about Keyman Developer. Just like developing keyboard for Windows, it is a similar process.
Please look into this link to get started: Create a simple touch keyboard.
Let us know if there is further question.