Higher Order Functions in Javascript at Five Levels

1. Child:

Imagine you have a toy robot. Normally, you give it simple commands like “go forward” or “turn right”. But what if you could teach your robot a new command? Like “do a dance”, and this command could mean “turn right, then go forward, then spin around”.

Higher-order functions are like teaching your robot new commands. You can tell them to do certain steps (other functions), and they can do those steps in the order you told them to. They can even remember those steps for later!

2. Teenager:

You know how you can put songs in a playlist and it plays one song after another? You can think of higher-order functions like a playlist, but instead of songs, it’s other functions. These functions can run one after the other, or one function can use the result of another function, just like how you might like a song because it was recommended based on a song you like.

3. College student (not a CS major):

In many fields, a “higher order” operation is one that uses other operations as input or produces them as output. In JavaScript, a higher-order function is a function that can take other functions as arguments, return a function as a result, or both. This can be very useful because it allows you to create more general and reusable functions, much like how a good theory can be used to explain many different phenomena.

4. Computer Science Undergraduate:

In computer science, a higher-order function is a function that does at least one of the following: takes one or more functions as arguments (i.e., procedural parameters), returns a function as its result. All other functions are first-order functions.

This is crucial for functional programming concepts like map, filter, and reduce, which are implemented as higher-order functions. They increase the modularity and reusability of your code.

5. Grad student/Colleague:

Higher-order functions are a fundamental concept in functional programming. They take other functions as arguments, return functions as results, or both. This enables you to write code in a declarative style, which is more concise and easier to reason about than imperative style. They also enable you to create function composition and currying, which are powerful tools for abstracting and organizing code.

For example, JavaScript’s Array.prototype.map is a higher-order function that takes a function as an argument and applies it to each element in an array, producing a new array. Functions like these are powerful abstractions that let you write complex operations in a very succinct and readable way.