How to access Visualforce JS methods and variables from a lightning component

Question

There are many lightning components are embedded in a Visualforce page. I've setup many global variables and JS functions to share the state with lightning components. However, it seems no way that a lightning component could access any global variable or JS method from it's parent contaniner(VF page)

Answer 1

This Communicating between Lightning Components and Visualforce Pages article that you may have seen explains:

Different Origins. Visualforce pages and Lightning Components are served from different domains. For example, if you are using a developer edition:

• Lightning Components are loaded from a domain that looks like this: yourdomain-dev-ed.lightning.force.com
• Visualforce pages are loaded from a domain that looks like this: yourdomain-dev-ed–c.na35.visual.force.com

The browser’s same-origin policy prevents a page from accessing content or code in another page loaded from a different origin (protocol + port + host).

In our case, that means that a Visualforce page can’t use the parent window reference to access content or execute code in the Lightning Component wrapper. Similarly, the Lightning component can’t use the iframe’s contentWindow reference to access content or execute code in the Visualforce page it wraps.

These restrictions are enforced for very good reasons. But fortunately, there is also an API (otherWindow.postMessage()) that provides a secure approach (when used properly) to exchange messages between different window objects with content loaded from different origins.

So best to think of these as two separate environments and to not attempt to build much logic that spans both.

However, when you have to, you can pass complex objects between the two via the postMessage mechanism where the message can be:

Data to be sent to the other window. The data is serialized using the structured clone algorithm. This means you can pass a broad variety of data objects safely to the destination window without having to serialize them yourself.