Section 4: Objects and Functions

Question 1

What values can hold an Object ? and how they are called?

Answer 1

A primitive that is called a property

An object that is called a property also

Functions that are called methods

Question 2

An object have reference in memory to their peorperties and methods?

Answer 2

YES

Question 3

How is important to think about an Object as…

(When we talk about how it´s an object in memory)

Answer 3

As sitting in memory, and then having references to other things sitting in memory that are connected to it, so it knows where its different properties and methods are, that is: primitives, objects and functions. (properties and methods)

Question 4

How can we access those slots in memory, those properties and methods of an object?

and how are their names(of the operators)?

Answer 4

With 2 operators:

the dot operator . also called member access

the computed memeber access operator []

Question 5

What does the computed member access operator [] ?

and help me to remember what an operator is, under the hood?

Answer 5

Remember, an operator is a function.

The computed member operator, takes two parameters and it’s associativity is left-to-right

to the left it takes the object, and inside the [] it takes the property or method

Question 6

What does the dot . operator do?

Answer 6

It’s a fnction and when used after an object it takes two parameters, the object that you’re looking at and the name of the property.

It takes the object(on the left) and on the right the string that represents the name of the value that you are looking for

Question 7

What is the other name of the dot . operator?

Answer 7

It´s also called Member Access

Question 8

Why the dot . operator is called Member Access

Answer 8

Because members being members of the object, These are looking for members of the object, the pieces, the methods, and the properties

Question 9

How can we create an object with object literals

Answer 9

using curly braces { }

Question 10

What is inside the curly braces { } how is it treated, how many lines of code?

Answer 10

It´s treated as one line of code

Question 11

When it gets really powerful to use object literals?

Answer 11

Because we can create objects on the fly

For example, on passing parameters to a function, as an object literal

Question 12

Let´s pass some object as a parameter to this function, how can we imagine this.

function greet(person) {

console.log(“Hi ” + person.firstname);

}

Answer 12

We can call the greet funciton, and create an object on the fly

greet({

firstname: ‘Tony’,
lastname: ‘Garcia’

});

Question 13

What “think” the JS engine when it sees:

greet({

firstname: ‘Tony’,
lastname: ‘Garcia’

});

Answer 13

it says:

“oh, you are calling a function, and oh, what are you gonna pass to it? Well, I just saw curly braces { } so I know you´re creating an object right here at this moment of execution and passing it, it`d be no different than passing anything else like a number or a string”

Question 14

It´s true to say that “Wherever i want I can create an object as I go, and I can use an object wherever I use any variable”?

Answer 14

YES

Question 15

What is a Namespace?

Answer 15

A container for variables and functions, typically to keep variables and functions with the same name separate.

Question 16

JS have namespaces? and why?

Answer 16

NO, because of the nature of how objects works inJS, we don´t need it as a feature

Question 17

How can we fake namespaces, for preventing collisions like this one:

var greet = “hello!”;

var greet = “hola!;

console.log(greet) // hola!

Answer 17

by creating an object that will be the container for our properties and methods and the things we want to use. The object it won’t really have any other functionality, and that’s okay

var english = {

greetings: {
basic: ‘Hello’

}

}

console.log(english.greetings.basic);

Question 18

What is the idea of using objects as faking namespaces? and why?

Answer 18

We need to containe variables, methods, functions, properties from the global namespaces.

Because someone else might have written or even that we´ve written code in the global namespace and forgotten about.

Question 19

What it means JSON, and what is JSON

Answer 19

Javascript object notation.

It´s just a string of data

Question 20

In a JSON format, how properties needs to be wrapped?

Answer 20

in quotes “ “

Question 21

JSON is a part of JS?

Answer 21

No

Question 22

Imagine a JSON format file, with two properties, how it will look?

Answer 22

{

“firstname”: “Mary”,

“isAProgrammer”: true

}

Question 23

How can we set a valid object literal in JS to a JSON format?

Answer 23

using the JSON.stringify() method

Question 24

How can we pass a valid JSON string of data, to an Object in JS?

Answer 24

using JSON.parse() method

Question 25

1) Anything that is JSON valid is also valid JS object literal syntax?
2) All object literal syntax is valid JSON?

Answer 25

1) YES
2) NO

Question 26

What is the meaning of “first class functions”

Answer 26

Everything you can do with other types you can do with functions. Assign them to variables, pass them around, create them on the fly

Question 27

In JS, functions are objects?

Answer 27

YES

Question 28

Does a function object resides in memory?

Answer 28

Yes, it resides in memory

Question 29

Does a function object, has all the features of a normal object and has some other special properties?

Answer 29

YEs

Question 30

Can you attach properties and methods to a function? and why?

Answer 30

Yes, you can.

Because it´s just an object

Question 31

Does function objects has some hidden special properties?

Answer 31

YES

Question 32

What are the hidden properties of a function object?

Answer 32

the code property

and the name property (it could also be anonymous)

Question 33

What does the code property of a function object do or have?

Answer 33

it has the actual lines of code that you´ve written.

So the code that you write gets placed into a special property of the function object.

Question 34

The code property of a function object, we can say that its like a …. of the function object

Answer 34

We can sey that its like a PROPERTY that you´re adding on to it

Question 35

What is the special thing about the “code property” of a function object?

Answer 35

It´s that is invocable, meaning that you can run the code that it´s in that property.

Question 36

What is the special thing that makes total sense in JS that happens when in a function object, you invoke the “code property” with the ()

Answer 36

It´s the execution context creation phase and execution happens.

Question 37

The code inside a function, it´s just a ….

Answer 37

The mental model of knowing that the code inside a function, it´s just a property, a “code property” like other property, that it´s invocable via (), meaning that the “code property” it´s going to be run.

Question 38

What is an expression?

Answer 38

a unit of code that results in a value, it doesn´t have to save to a variable

Question 39

What is the difference between a function statement and a function expression?

Answer 39

a function statement just do work

a function expression or any expression in JS ends up creating a value and that value doesn´t necessarily have to save inside a variable

Question 40

function expressions are hosited?

Answer 40

no, it just hoisted the variable

Question 41

What happens in the execution phase when it gets to a function statement

Answer 41

function statement: the function is already in memory, so it doen´t do anything “oh yeah, there´s a function there, it keeps going”

Question 42

What happens in the execution phase whe it gets into a function expression?

Answer 42

the statement results in an object being created, it returns an object essentially, so it´s an expression, it results in a value, the value being a new function object

Question 43

When we pass values “by value” what do we mean:

ej:

var a = 3;

var b = a;

Answer 43

We are creating a new address in memory, a new location in memory, and a copy of the value from “a” is setting in “b”

It´s a completely new value

Question 44

When we pass a value “by reference” what do we mean?

Answer 44

We are setting a reference to the value, the new variable has a reference to the same spot in memory that the original variable has

Question 45

When we talk about “by value” and “by reference”

Which one apply to whicn one

Primitives and objects types

Answer 45

Primitives, are passed by value

Objects, and function objects(a special type of object) are passed by reference

Question 46

What happens when we use the keyword “this” inside a function statement, to where “this” will point

Answer 46

It will point to the Global Object

Question 47

What happens when we use the keyword “this” inside a function expression, to where “this” will point

Answer 47

It will point to the Global Window Object

Question 48

What happens when we use the keyword “this” inside an object, to where “this” will point?

Answer 48

to the object itself, the object that is containing “this”

Question 49

What happens when we have the “this” keyword inside a function expression, inside a method of an object, to where it will point?, and why?

var c = {

name: ‘The c object’,
log: function() {
console. log(this);

var setName = function(newName) {

this.name = newName;

}

setName(“updated again”);

console.log(this); // added the name property into the Window Object

}

}

Answer 49

It will point to the Global Object

Why? The internal function setName(), when its execution context was created, the “this” keyword points to the global object.

Question 50

What can we do when we have the “this” keyword inside a function, that it´s inside a method of an object, how can we resolve the porlbme that the “this” keyword is pointing to the global object?

Answer 50

We know that an object are going to be set equal by reference, so we can create a new variable and reference it to the same location in memory as the “this” keyword

var c = {

name: ‘The c object’,
log: function() {

var self = this;

console.log(self);

var setName = function(newName) {

self.name = newName;

}

setName(“updated again”);

console.log(self); //

}

}

Question 51

Any internal function inside a method in an object, that is using the keyword “this” will be pointing to the Global Object, or to the object itself?

Answer 51

It will be poiting to the global object

Question 52

What is an array?

Answer 52

Its a collection of anything, it can holds many things

Question 53

How can we declare an array using array literals

Answer 53

var a = [1, 2, 3];

Question 54

Complete the sentence

Because JS is …… ….. we can put anything into an array

Answer 54

dynamically typed

Question 55

Function expressions are like a kind of a function literal were we are creating a function on the fly?

Answer 55

YES

Question 56

How can we trick the syntax parser to see a function statement like a function expression?

Answer 56

We have to make sure that the first thing that the syntax parser see, its not the word function, so we need to wrap the function with ( ) the grouping operator

Question 57

Why when we wrap a function statement with ( ) the grouping operator, the syntax parser doesn´t give an error?

Answer 57

Because everything that goes into the grouping operator ( ) it´s an expression. We only use ( ) with expressions.

Question 58

What “think” the syntax parser when it sees a funciton statement inside the grouping operator ( )

Answer 58

it must me an expression, it must be a function expression, the programmer its creating this function “on the fly”.

Question 59

How can we make a IIFE immediately function expression?

Answer 59

We need to wrap a function statement with the grouping operator ( ), and since a function, it´s a special type of object in JS, we can invoke the code property with (), so we must use the invoke sytanx at the end of the grouping operator

(function(name) {

return ‘Hello ‘ + name;

})();

Question 60

What is the purpose of having an IIFE?

Answer 60

To protect our code from other outside code

To prevent us to put something accidentally in the global object

Question 61

How can we pass information from our IIFE into the global object?

Answer 61

simply passing around parameters, objects pass by reference, so if we want access to the global object, we just pass the reference to the global object into our function

(function(global, name) {

var greeting = ‘Hello’,

global. greeting = “hola”,
console. log(greeting + ‘ ‘ + name);

})(window, ‘John’)); // Hello John

that´s the way to have our code, maybe some object in our function that we want to be available everywhere else in our code, we can stick it on the global object.

Question 62

Why we can return a function as a value?

Answer 62

Because functions are objects, are first class functions, a special type of object

Question 63

Que es un closure?

Answer 63

Los closures son funciones que manejan variables independientes. En otras palabras, la función definida en el closure “recuerda” el entorno en el que se ha creado.

Es crear una función dentro de otra función para que cuando cuando busque variables, estas sean independientes porque las busca en su propia referencia externa, porque cada función (la primera en ejecutarse) crea su propio contexto de ejecución.

Nos sirve para tener una “factory function” funciones creadoras de funciones.

Question 64

What is a callback function?

Answer 64

A function you give to another function, to be run when the other funciton is finished.

So the function you call(invoke) calls back, by calling the function you gave it when finished

function tellMeWhenDone(callback) {

var a = 1000;

var b = 2000;

callback(); // the callback, it runs the function we give it

}

tellMeWhenDone(function() {

console.log(‘done!’);

});

tellMeWhenDone(function() {

console.log(‘really done!’);

});

Question 65

What does the bind() method

Answer 65

returns a new function(makes a copy of the function, and sets up a new function object with the copy), and sets “this” to whatever object we want.

Question 66

what does call()

Answer 66

let me decide what “this” will be, and i can pass arguments to it

call() doesn´t create a new function, it works as if we invoke it

Question 67

what does apply()

Answer 67

executes a function, deciding what “this” should point to, the arguments must be passed with an array list

Question 68

What method can we use for doing “Function borrowing”, and give one example

Answer 68

call() and apply()

For function borrowing, when we want to use a method from one object, on another object!

Question 69

What method can we use when we want to do “function currying”? and why

Answer 69

We can use bind() method, because bind creates a new copy, and since its a new copy of the function object, the parameters that we pass sets the permaments values of these parameters when the copy is made!

function multiply(a, b) {

return a \* b;
}
var multipleByTwo = multiply.bind(this, 2);
console.log(multipleByTwo(4)); // 8

// The permament value of the second parameters b will be always 2

function multiply(b) {

var a = 2;

return a * b;
}

Question 70

What means, function currying?

Answer 70

Creating a copy of a function but with some preset parameters

Question 72

To where points “this” in this case

function asdf() {

console.log(this);

}

Answer 72

To the global windows object.

Question 73

What we need to look at when we have the “this” keyword inside a function or object, to where it its pointig to?

Cómo nos podemos dar cuenta hacia donde apunta “this” cuando estamos invocando una función o metodo que esta usando a la palabra “this”.

Answer 73

Podemos fijarnos como es invocada esa funcion / metodo

el operador dot . es el que nos va a avisar hacia donde apunta, si tiene algo a su izquierda, es ese objeto, si se invoca sin punto, generalmente es el objecto global window

Question 74

Describe what is “this”(to where it points) in the following scenarios:

1) Inside a method of an object
2) Inside a function statement
3) Inside a function expression
4) An internal function, that it´s located inside a method of an object

Answer 74

This points to:

1) The object itself, the object that is calling the method
2) global variable window
3) global variable window
4) points to the global variable( lot of people think this is a bug)

Question 75

What is one of the purposes of making a function factory?

Answer 75

To have variables inside and secure in a closure

Question 76

Answer 76

We are making use of closures

greetEnglish, will return a function, will be a function where “var language = en”

Tx to closures, when greetEnglish is invoked, and it creates its own execution context it will still have the var “en” inside their clousure.

So greetEnglish is a function object whose closure points to language being en

Question 77

How can we create a function factory that is going to be using always the parameters that we pass?

What could happend if we pass variables as parameters to a function that return another function.

Answer 77

Using a function factory, and returning a function

When we return a function from a function, we are creating a closure.

When the returning function executes it creates itw own execution context, and its outer reference will point to the execution context that was created when invoking this function that returned this function (That´s a closure)

Question 78

What is the key to understandin closures?

Every time you call a function…

Answer 78

it gets itw own execution context,, and any function created inside of it will point (outer reference) to that execution context.

It wil point to the memory space, as if those other execution context hadn´t disappeared.

It knows which ones to point to properly, where these inner functions were created and when.

Question 79

For what are useful the function factories?

Answer 79

To stop passing parameters that could be used as default

var greetEnglish = makeGreeting(‘en’) // makeGreeting returns a function

greetEnglish(‘Bruno’, ‘De Angeli’); // greetEnglish has the returned funciton with the language set by default, tx to closures.

Question 80

How creates a closure, the JS or us?

Answer 80

TheJS creates the clousure, its a feature, we are just taking advantage of it.

Question 81

When the execution context that was actually running finish his execution and goes away…

1) What happens to that memory space where the variables and functions created inside of it live?
2) And how this relate to closure and “function factories”

Answer 81

1) It still continues in memory…
2) It relate to closure in the way that if we are returning a function from a function, and the first function execution context is gone, and we execute the second execution context(from the function that was returned from the first function) we still has a reference to the memory of the first function. We can still go down the scope chain and find it
- We can say that the execution context has closed IN its outer variables, the variables that it would normally have reference to anyway, even though those execution context are gone

That´s a closure, and that´s why we can make function factories

Question 82

What is the meaning of free variables, and when it comes natural to get them?

Answer 82

its natural to get them when we are inside a closure.

It is a variable that is outside a function, but that you have access to.