Functions: Closures, HOF and Prototypes

Question 1

Why is Function First class citizens?

Answer 1

1. We can assign it to the variable
2. Pass it as a variable
3. Return it as a variable

Which is not possible in many languages.

Question 2

What is function constructor?

Answer 2

const four = new Function(“return 4”)
four() // return 4;

const num = new Function(“a”, “b”, “return a+b”);
num(4,5) // return 9;

The last parameter is always the code.

Question 3

What happens in Function execution context?

Answer 3

Function Execution context has this, arguments and all looks at the variables and store them in memory heap.

Question 4

How is function an object in javascript?

Answer 4

Functions are stored in javascript as special objects callable objects.
There is an internal property, [[Call]], that determines what will be executed when the object is called.

Function constructor
const num = new Function(“a”, “b”, “return a+b”)
num.foo = 3;

Question 5

What are callable objects in javascript?

Answer 5

Functions are stored in javascript as special objects callable objects.

There is an internal property, [[Call]], that determines what will be executed when the object is called.
Plain objects don’t have this internal property, so they aren’t callable, and can’t be made to be callable.

The only callables in JS are functions (which are also objects), classes (which are actually functions, and therefore objects as well), and Proxy objects that wrap callables.

Question 6

What does function object in javascript contain?

Answer 6

In JavaScript, functions are first-class objects, because they can have properties and methods just like any other object.

Function has:
Name: Name of the function.
paraments: The name of an argument to be passed to the function.
statements: The statements comprising the body of the function.
Properties: call(), apply(), bind(), etc..

Question 7

What is Higher ordered function?

Answer 7

Higher order function:
A higher-order function takes a function as an argument, returns a function, or both.

Question 8

What and when do we use is Higher order function?

Answer 8

A Higher Order FuncBon (HOF) is a function that either takes a function as an argument or returns another function.

Example of the HOF.

Question 9

Example of HOC?

Answer 9

Question 10

What are the 2 pillars of Javascript?

Answer 10

1. Closure
2. Prototypal Inheritance

Question 11

What is a closure?

Answer 11

A closure combines a function bundled together (enclosed) with references to its surrounding state (the lexical environment).

function init() {
var name = ‘Mozilla’; // name is a local variable created by init
function displayName() {
// displayName() is the inner function, a closure
console.log(name); // use variable declared in the parent function
}
displayName();
}
init();

Question 12

What is a difference between closure & HOC?

Answer 12

Higher order function:
A higher-order function takes a function as an argument, returns a function, or both.

Closure:
A closure combines a function bundled together (enclosed) with references to its surrounding state (the lexical environment).

So a function can be closure and HOF.

PFA image of HOF and Closure combined.

Question 13

Can you write an example of closure?

Answer 13

// Explanation of closure
/* 1 / function foo()
/ 2 / {
/ 3 / var b = 1;
/ 4 / function inner(){
/ 5 / return b;
/ 6 / }
/ 7 / return inner;
/ 8 / }
/ 9 / var get_func_inner = foo();
/ 10 / console.log(get_func_inner());
/ 11 / console.log(get_func_inner());
/ 12 */ console.log(get_func_inner());

Explanation: Note line number 9 to line number 12.
At line number 9, we are done with the execution of function foo() and the entire body of function inner() is returned and stored in var get_func_inner due to the line 7 return inner.

We can access the variable b which is defined in function foo() through function inner() as the later preserves the scope chain of enclosing function at the time of execution of enclosing function i.e. the inner function knows the value of b through it’s scope chain.

Question 14

How do you see closures in console?

Answer 14

By using console.dir to the parent function.

Question 15

What is scope chaining?

Answer 15

Scope chaining is how the variables are passed from the parent function to the
As we can see, the variables within the closure in the scope section.

Question 16

How do we make closure memory efficient?

Answer 16

In the example in picture, big array is only created once and used multiple time in with closures.

Question 17

What is encapsulation?

Answer 17

Encapsulation means the restriction of direct access to some of an object’s components. It hides as much as possible of an object’s internal parts and only exposes the necessary parts to run. Why use encapsulation?

• Security - Controlled access
• Hide ImplementaBon and Expose Behaviours
• Loose Coupling - Modify the implementation at any time

Question 18

How to encapsulate with closures?

Answer 18

In this example, there is no direct access to the data people array in the closure. using set, get and remove we are manipulation and fetching the data.

Question 19

How do you solve this?

Answer 19

We can solve it by using let so by using IIFE (Immediately Invoked Function Expression)

Question 20

What is the difference between IIFE and Closure?

Answer 20

IIFE helps avoid global variable pollution when multiple functions are accessing a global variable
Closure functions are helpful when working with a local variable.

Question 21

What is Prototype?

Answer 21

Array and Functional are Objects. But they get these properties because of Prototypal Inheritance.

Example:
arr = []

arr.__proto__
In console.log, you will find methods like push, pop and slice.

And if you do
arr.__proto__.__proto__
You will find methods like toString object; because of prototype chaining, we can use the “toString” method directly in the array.

In the case of a function, it points to native function which points to an object.

Question 22

In Javascript do we have class?

Answer 22

Javascript doesn’t have class, it has the prototypal inheritance. In ES6, we use class which compiles down to these prototypes.

Question 23

What is the different between bind and prototypal inheritance?

Answer 23

With bind, you can bind a few properties, but can’t inherit the entire object.

Question 24

What is prototype chain?

Answer 24

Each object has a private property which holds a link to another object called its prototype. That prototype object has a prototype of its own, and so on until an object is reached with null as its prototype.

So basically it’s a linked list to the parent object prototype.

Question 25

How do we write prototypal inheritance with an example?

Answer 25

let father = { surname: “Ch”, language : “English” }
let mother = { language : “Telugu” }
let son = { }
mother.__proto__ = father
son.__proto__ = mother

son.language // will be telugu.

mother.isPrototypeOf(son) // true
father.isPrototypeOf(son) // true
son.isPrototypeOf(father) // false
son.isPrototypeOf(mother) // false

Question 26

How to check the properties of the function?

Answer 26

Using “hasOwnProperty(propName)”

For list of all the properties we can loop the object.

Question 27

What is the difference between lexical scopes vs prototype scopes?

Answer 27

Lexical scopes are passed from parent to child.
Prototypes are inherited to parent to child.

Question 28

Is is a good approach to directly use __proto__ to assign and inherit?

Answer 28

No, it’s not and it’s a terrible approach for performance

Question 29

What is the difference between prototype and __proto__?

Answer 29

__proto__ points to the “prototype” up the chain.
__proto__ lives in the same object lives in “prototype”.

const arr = []

arr.hasOwnPropety(“map”) // return false.
arr.__proto__.hasOwnPropety(“map”) // return true.

So map should live only in one location in the memory

Question 30

How to create a prototype a safe way?

Answer 30

Which Object.Create

let human = { mortal: true }
let socrates = Object.create(human)
socrates.age = 45
console.log(human.isPrototypeOf(socrates))

Question 31

Imposter Syndrome?

Answer 31

Teaching while we learn is important thing.