innerFunction

An innerFunction, in programming, is a function defined within the body of another function (the outer function). Inner functions are common in languages with first-class functions and lexical scoping.

An innerFunction has access to its own local variables, the parameters of the outer function, and any variables in the outer function's scope. This enables closures, where the inner function retains access to these bindings even after the outer function has completed execution.

They are often used to create helper routines, implement factory functions, or to create function closures that carry state. In many languages, inner functions are not accessible from outside unless explicitly returned or assigned.

Examples include Python, JavaScript, and other languages with lexical scoping and first-class functions. They can be anonymous or named, and may be assigned to variables, passed as arguments, or returned as values.

In some languages, references to outer variables require nonlocal or similar declarations; inner functions may impose scope-related restrictions. Use inner functions to encapsulate implementation details, avoid polluting the outer scope, and to create clean interfaces.

See also: closures, lexical scope, first-class functions.