A "function within a function" and a "closure" are related concepts, but they have distinct differences:
Function within a Function:
- This refers to a function that is defined inside another function.
- The inner function can access variables and parameters of the outer function, but it does not necessarily create a closure.
- The inner function can be invoked only within the scope of the outer function.
- Once the outer function finishes executing, the inner function's access to the outer variables may be lost.
- A closure is created when an inner function "closes over" its surrounding lexical (scope) environment, capturing and retaining access to variables even after the outer function has finished executing.
- Closures allow the inner function to access and "remember" the variables of its outer function, even outside the outer function's scope.
- Closures are not limited to being invoked only within the scope of the outer function; they can be passed around and invoked from different places, preserving access to the captured variables.
every closure is an example of a function within a function, but not every function within a function creates a closure. A closure specifically occurs when an inner function maintains access to its enclosing scope, allowing it to access variables from the outer function even after that function has completed its execution.