Takaisinkutsut

Takaisinkutsut (callbacks) are a programming pattern in which a function is passed as an argument to another function and is invoked later, often in response to an event, completion of an asynchronous task, or user action. The passed function is called back by the callee when the triggering condition occurs, allowing the caller to specify behavior to run at that moment without blocking.

In practice, callbacks are central to event-driven and asynchronous programming. Common use cases include handling user input, responding to I/O completion, timers, and network requests. In languages like JavaScript, a callback is supplied as a parameter and is executed when a task finishes; in Node.js, callbacks frequently follow the error-first convention: the first parameter represents an error (if any), and subsequent parameters carry the result.

Design considerations: callbacks enable non-blocking operations but can lead to deeply nested code, often referred to as callback hell. Techniques to mitigate this include naming callbacks clearly, modularizing code, and adopting higher-level abstractions such as promises and async/await, which unify asynchronous flows and improve readability. Some languages provide dedicated constructs or APIs for events or signals that accomplish similar goals with different syntax.

Global usage: callbacks are widely used across programming languages, including JavaScript, Python (for asynchronous tasks or GUI frameworks), C and C++ (function-pointer callbacks), and Java (event listeners). Understanding the callback model aids in designing responsive, modular software.