anonymous function

Anonymous functions, also called closures, allow you to temporarily create a function without a specified name. The value most commonly used as a callback function argument. Of course, there are other applications as well.

Implementation structure

## Closure: Put the anonymous function in a normal function, or you can return the anonymous function, which forms a simple closure

Keywords: use connects the variables and values ​​of the context

Application scenarios of closures:

①, to protect the safety of variables within the function. The variables in the outer function can only be accessed by the inner function, and cannot be accessed through other means

②. The variables in the outer function always exist in the memory, so they will be used every time it is executed.

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