Understanding of closures

The essence of a closure is a chain of scopes formed by nesting functions

The definition of closure is ： function A There's a function inside B, function B You can access functions A The variables in the , So the function B It's a closure

z Be careful ： Closure , Variable Promotion , Variables are brought forward to the function , But not assigned

The benefits of the bag ：

1. You want variables to reside in memory for a long time （ General functions have been executed , Variables and parameters are destroyed ）

2. Avoid pollution of global variables