Higher-order Functions

An introduction to functional programming.

In order to write great code in JavaScript or even understand frameworks written in this language, it’s vital to understand the meaning of “Higher-order Functions”.

Functions that operate on other functions, either by taking them as arguments or by returning them, are called higher-order functions.

Eloquent JavaScript Or simply; in JavaScript, we can pass functions as an argument to other functions and receive a function as a result of their execution.

var employees = [{
    name: 'Alfie Atkins',
    position: 'Programmer'
}, {
    name: 'Torill Kove',
    position: 'Director'
}];

var programmers = employees.filter(function (employee) {
    return employee.position === 'Programmer'
});

After all, unlike OOP languages, Functions in JavaScript can exist on their own without any dependency on a class. That’s why we call them “first-class citizens”. They are objects (just like OOP class instances), and objects can be assigned to variables.

Therefore to make things even simpler, let’s say that: in JavaScript, functions are values (just like numbers and strings).

var foo = function () {
    console.log('Hello World!');
}

foo();

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