I've been getting into JS, but one thing still confuses me. I'm sorry for not explaining it very well, but if you type console.log(window); onto the console on https://scratch.mit.edu you get something like this:

What I'm wondering is what is the label in front of the {} in window.caches and window.clientInformation, and what is it used for?

if i understand your question correctly, thats a custom object type. you can make your own with the new operator.