How do JavaScript closures work?
A closure is an inner function that has access to the outer (enclosing) function’s variables—scope chain. The closure has three scope chains: it has access to its own scope (variables defined between its curly brackets), it has access to the outer function’s variables, and it has access to the global variables.
The inner function has access not only to the outer function’s variables, but also to the outer function’s parameters. Note that the inner function cannot call the outer function’s arguments object, however, even though it can call the outer function’s parameters directly. You create a closure by adding a function inside another function.
Closures have access to the outer function’s variable even after the outer function returns.
Closures store references to the outer function’s variables.
Closures have access to the updated values of the outer function’s variables, they can also lead to bugs when the outer function’s variable changes with a for loop. To fix this side effect (bug) in closures, you can use an Immediately Invoked Function Expression (IIFE).