This content originally appeared on DEV Community and was authored by Nikita Kozlov
Question:
Explain Higher Order Functions in javascript.
Quick answer:
These are functions that return other functions.
Longer answer:
In JavaScript, you can return objects of any type as a result of the function. This means you can create a function that will return a function.
function higherFunction() {
return function regularFunction() {
console.log('Hello world!')
}
}
const a = higherFunction() // won't print anything
a() // Hello world!
You can also try to create even more nested functions.
const a = () => () => () => () => console.log('Hello world')
const b = a()
const c = b()
const d = c()
d() // Hello world!
You can pass functions to a function that will execute functions in some specific order.
const pipe = (...args) =>
(init) =>
args.reduce((acc, cur) => cur(acc), init)
const a = pipe(
(val) => val + 1,
(val) => val * 2,
(val) => console.log("Got", val),
)
a(10) // Got 22
And more other fun ways to use functions ?
Real-life example:
Some frameworks (angular) and libraries (MobX) heavily rely on decorators, but decorators are no more than Higher Order Functions themselves.
const logDecorator = (wrapped) => {
return (...args) => {
console.log(`Invoked ${wrapped.name} with args ${args}`)
wrapped(...args)
}
}
const tmp = (param) => {
console.log('Do nothing, but just show param:', param)
}
const wrappedTmp = logDecorator(tmp)
wrappedTmp('Hello world!')
// Invoked tmp with args Hello world!
// Do nothing, but just show param: Hello world!
Some other libraries (RxJs) may use it as configurable helpers.
// These functions can by provided by a library itself
const uppercase = (a) => a.toUpperCase();
const removePunctuation = (a) => a.replace(/[^0-9a-zA-Z ]/g, '')
// pipe is a Higher Order Function that returns a function, which will apply all functions one by one
const process = pipe(
uppercase,
removePunctuation,
)
console.log(process('qwe-qwe'), process('Hello world!'))
// QWEQWE HELLO WORLD
Btw, I will post more fun stuff here and on Twitter. Let's be friends ?
This content originally appeared on DEV Community and was authored by Nikita Kozlov
Nikita Kozlov | Sciencx (2021-04-26T10:52:48+00:00) JS interview in 2 minutes / Higher Order Functions. Retrieved from https://www.scien.cx/2021/04/26/js-interview-in-2-minutes-higher-order-functions/
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