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Higher-Order Functions
Introduction

We are often unaware of the number of assumptions we make when we communicate with other people in our native languages. If we told you to “count to three,” we would expect you to say or think the numbers one, two and three. We assumed you would know to start with “one” and end with “three”. With programming, we’re faced with needing to be more explicit with our directions to the computer. Here’s how we might tell the computer to “count to three”:

for (let i = 1; i<=3; i++) { console.log(i) }

When we speak to other humans, we share a vocabulary that gives us quick ways to communicate complicated concepts. When we say “bake”, it calls to mind a familiar subroutine— preheating an oven, putting something into an oven for a set amount of time, and finally removing it. This allows us to abstract away a lot of the details and communicate key concepts more concisely. Instead of listing all those details, we can say, “We baked a cake,” and still impart all that meaning to you.

In programming, we can accomplish “abstraction” by writing functions. In addition to allowing us to reuse our code, functions help to make clear, readable programs. If you encountered countToThree() in a program, you might be able to quickly guess what the function did without having to stop and read the function’s body.

We’re also going to learn about another way to add a level of abstraction to our programming: higher-order functions. Higher-order functions are functions that accept other functions as arguments and/or return functions as output. This enables us to build abstractions on other abstractions, just like “We hosted a birthday party” is an abstraction that may build on the abstraction “We made a cake.”

In summary, using more abstraction in our code allows us to write more modular code which is easier to read and debug.

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