Functions in JavaScript are first-class citizens of the language just like Objects.

Functions enjoy all the same privileges (in fact more) as do the Objects in JavaScript.

Privileges such as

1. Functions can be created via a literal notation.

var obj = {a : 2, b: 2}; // object literal

var add = function(a, b) { // function literal
    return a + b;
};

2. Functions can be assigned to variables, array entries and object properties.

var add = function(a, b) { // function assigned to a variable
    return a + b;
};

var arr = [];
arr[0] = add; // function assigned to array entry at index 0

var obj = {};
obj.addMethod = add; // function assigned to Object obj as a addMethod property

3. Functions can be passed as arguments to other functions.

var values = [34, 56, 12, 11 , 5, 123];

var descendingComparator = function(value1, value2) {
    return value2 - value1;
}
values.sort(descendingComparator); // function descendingComparator passed as argument

console.log(values); // this should print [123, 56, 34, 12, 11, 5]

4. Functions can be returned as values from other functions

function multiplier(x) {
    return function(y) { return x * y;};
}

var doubleIt = multiplier(2);
console.log(doubleIt(2)); // prints 4

var tripleIt = multiplier(3);
console.log(tripleIt(3)); // prints 9

5. Functions can also have their own properties and these properties can be added or removed dynamically

function myFunc() {}

myFunc.prop1 = 'prop1';

console.log(myFunc.prop1); // prints prop1

In addition to all of the above, Functions also have a special superpower in that they can be invoked