On the right-hand side, you can define dynamic parameters inside a Stored Function in CustomJS. All dynamic parameters you create here are accessible via input.PARAMETER_NAME. In Make, they will automatically appear once you load the function using the Execute a Stored Function module.
You can then easily use these parameters in your JavaScript code by referencing them through the input variable.
You can retrieve JSON data directly from the Input field in a CustomJS Function but you have to parse it with JSON.parse().
In Make, you need to build a proper JSON object as a string, or construct it using Make modules. Be careful you have to convert Make collections into a JSON object by using the Transform to JSON module. Learn more