JavaScript SPA: How to identify a module/component?

I came across several JavaScript Frameworks/Libraries for building Webapps. Most of them have conecepts to encapsulate specific parts of the application code into modules or components - so far, everything makes sense to me.

My problem is: If i have the set of requirements for my webapp, how would i identify the parts to seperate in different modules or components? Which questions should i ask myself? What is the pattern to follow during design process?

Lets say i want to develop a new blog software like Wordpress (don't worry, it is just an example). Which parts of the application could be modules/compoentes for themself?

I would be happy with some insights of more experienced developers on this topic.

Thanks in advance!