window.variableName

Question

I am going through some code and at the beginning of the script we have var emailID = email. Later on, the code refers to emailID by going window.emailID<

Answer 1

Global variables in JavaScript are attached to the "global object", which in a browser environment is aliased to window object - this is why you can refer to a global variable either as variableName or window.variableName.

It's also worth mentioning that using global variables in JavaScript is not considered good coding practice.

Here's a good and very detailed explanation.