Why do browser Javascript libraries pass the window object as an argument?

Question

While looking at various JavaScript libraries, I have noticed a relatively common practice of passing either the window or the document object as part of the arguments given to the library initialization function.

Examples:

• DOM4
• ContentLoaded
• EasyXDM
• fingerprintjs

While I understand very well why that would be done for libraries that are designed to run on non-browser environments, I do not know why that is done for libraries that seem designed only for client browser environments. (Such as all the examples given above).

Answer 1

It also helps to speed up the library as window or document is now locally bound. And this also ensures that if latter the user, replaces the window object with say: window = "Help, I'm trapped in a window overwriting assignment statement.";; the library continues to work.