JavaScript Higher-Order Functions: A Complete Guide

Higher-order functions in JavaScript are presented as an extension of functional programming, where functions are first-class citizens. The article explains that this makes it possible to pass functions as arguments, return them from other functions, or do both in the same pattern.

It also frames higher-order functions as a way to abstract over actions. The examples cover creating new functions, changing how a function is called by supplying its arguments separately, and defining control flow with custom helpers. The post ends by listing built-in higher-order functions such as map, filter, reduce, forEach, and addEventListener, and by noting their benefits for reuse, clarity, debugging, and code composition.

Reading notes

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• JavaScript is described as a multiparadigm language that supports functional programming.
• Functional programming is linked to handling pure mathematical functions and structuring code with functions.
• Functions are treated as first-class citizens, so they can be assigned to variables, stored in arrays, set as object properties, and passed around as arguments or return values.
• A higher-order function can take one or more functions as arguments, return a function, or do both.
• One example shows a function that applies another function to each item in an array.
• Another example shows a function that returns a second function and keeps access to the outer function’s data.
• A combined example shows a function that both receives a function parameter and returns another function.
• Higher-order functions are also used to abstract over actions, not only values.
• One example creates a function that filters array elements greater than a given value.
• Another example changes how a function is used by passing it through a wrapper that supplies its arguments later.
• A custom control-flow example uses one higher-order function to decide when another callback should run.
• The article lists built-in higher-order functions in arrays, strings, DOM methods, promise methods, and related APIs.
• The benefits mentioned are abstraction, reuse, simpler code, easier debugging, and more compact composition.