First Class Functions

11.04.2020 — Functional Programming, JavaScript

If you are a JavaScript programmer this term should be quite familiar to you. Maybe you even don't know that in your daily work you are using with First Class Functions.

When the functions are treated like any other value in the programming language, that's mean that they are First Class Functions.

Functions can be stored in variables

const log = console.log
const add = (...args) => args.reduce((x, y) => x + y, 0)

Functions can be stored in arrays

const queue = 
[
  () => console.log('foo'),
  () => console.log('bar'),
  () => console.log('baz')  
]
queue.shfit()()

Functions can be passed as arguments to the other functions and return them

const onError = error => throw err 
const onSuccess = data => console.log(data)
fs.readFile(onError, onSuccess)

Functions can be stored as a value of the object property

const obj = {
    foo: function foo () { return 'foo' },
    bar: function () { return 'bar' },
    baz: () => 'baz'
  }

Functions can be created using constructor like other objects

const fn = new Function('a', 'b', 'return a * b');
fn(5, 6)