Js static scope function.

JS scope is a complicated thing.

The JS scope is static. when defining a function, the function scope defines the scope of the function, rather than the scope of the function.

When a function is called, a new scope is created. The variable defined by var in this scope is a local variable, generally, after the function is executed, the created scope will be recycled by the system.

When defining a function trap, if the function defined in it is saved (for example, assigned to a global variable ). Then, the scope of the function (the scope created when the external function is called) must be saved together (that is, the scope created during the call at the end of the external function execution will not be recycled by the system, wait until the stored function is recycled by the system ).
All local variables stored in the scope are also saved.