Closures

Summary

A function that 'remembers' variables from the scope it was created in, even after that outer function has finished running — the basis of private state and many patterns. Closures allow functions to retain access to lexical state and are central to callbacks, factories, event handlers, encapsulation, memoization, and asynchronous code.

• 1Write a counter function that returns an increment function using a closure. Validate your understanding by applying it in a small practical example.
• 2Explain in your own words why closures 'remember' outer variables. Validate your understanding by applying it in a small practical example.
• 3Spot closures in real code — debounce, memoization and module patterns all use them.