The answer
Chaining small functions into a pipeline. compose(f, g) returns a function that does f(g(x)). This lets you build complex behavior from simple, reusable functions. It relies on functions being first-class (passable and returnable).
Functions as Arguments and Return Values in JavaScript
What is function composition in JavaScript?
More FAQs in Functions as Arguments and Return Values in JavaScript
Yes. This is a callback. setTimeout, map, filter, reduce, event listeners, and fetch.then all accept functions as arguments. The receiving function (higher-order) calls the callback at the right time.
Yes. A function that returns another function is a higher-order function (a function factory). The returned function often closes over the outer function's variables, creating a closure.
A function that takes a function as an argument, returns a function, or both. Examples: map, filter, reduce, compose, curry, partial, setTimeout, and event listeners.
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