Understanding of closures

How did it come into being ?

The variables of the outer function are referenced by functions nested inside the function body , The external variable cannot be released , It forms a closure .

effect ？

When an external wants to access an internal variable , But I don't want to define a global variable to cause global pollution , You can use closures .

shortcoming : Closures close normal functions with one more scope object , A normal function has only two scoped objects , One is the variable defined inside the function itself , The other is a global variable , Closures are multiple objects of an outer function scope , So it takes up more space than normal functions .