Todo

Question 1

Dynamic Typing

Answer 1

You don´t tell the engine what type of data a variable holds, it figures it out while your code is running. Variables can hold different types of values because it`s all figured out during execution

Question 2

What keyword exist to tell the engine what kind of data you intend to put inside a variable?

Answer 2

There is NO keyword

Question 3

What is a primitive Type?

Answer 3

A type of data that represents a single value

Question 4

An object is a primitive type?, and why?

Answer 4

not, because an object is a collection of name / value pairs

Question 5

How many primitive types exist in JS

Answer 5

6 primitive types

Question 6

Name the 6 primitive types in JS

Answer 6

undefinednullbooleannumberstringsymbol

Question 7

Describe the primitive type: Undefined

Answer 7

Represents lack of existence, its what the JS engine sets variables to initially and it will stay undefined unless you set the variable to have a value.

Question 8

Describe the primitive type: Nulland when its useful

Answer 8

represents lack of existence (you can set a variable to this).its useful when you want to represent that something doesn´t exist, that the variable has no value(set a variable to nothing).

Question 9

Describe the primitive type: Boolean

Answer 9

Either true or false, just one of two values

Question 10

Describe the primitive type: NumberExist other numeric types in JS?

Answer 10

There’s only one numeric type.Its a floating poing number (theres always some decimals)

Question 11

Describe the primitive type: StringWhat we use to define a string?

Answer 11

A sequence of characters (both ‘’ and “” can be used)

Question 12

Describe the primitive type: Symbol

Answer 12

It`s defined in ES6

Question 13

What is an operator?

Answer 13

It`s a special function that is syntactically (written) differently. Generally operators take 2 parameters and return one result.

Question 14

How did the JS engine that this was my intent to add 3 and 4?var a = 3 + 4;console.log(a); // result: 7

Answer 14

The syntax parser saw the plus(+) sign and added these 2 numbers.The plus sign is an operator, it’s actually a function.

Question 15

What is the name of the notation that the JS engine provide to deal with operators.

Answer 15

Inflix notation

Question 16

What it means “inflix notation”

Answer 16

Inflix mean that the function name, the operator, sits between the 2 parameters.

Question 17

When we type these operators, +, -, >, How these operators works?

Answer 17

These operators are a special type of functions, that the parameters between the operators are being passed to those functions and a value is being returnedInside those functions is prewritten code, for you that the JS language provides to do or run, or invoke these functions.

Question 18

What is operators precedence?

Answer 18

It´s which operator function gets called first, functions are called in order of precedence (HIGHER precedence wins)

Question 19

What is operator associativity?

Answer 19

What order operator functiosn get called in: left-to-right or right-to-left, and this means when the operator functions have the same precedence

Question 20

What is the purpose of operator precedence and associativity?

Answer 20

help us determine which function run first and so does associativity.

Question 21

When comes into play operator associativity?

Answer 21

Associativity comes into play when two or more operators have the same precedence

Question 22

What is coercion?

Answer 22

It´s converting a value from one type to another.

Question 23

Why coercion happens in JS?

Answer 23

Because it´s dynamically typed

Question 24

How coercion and operators relate, and what we need to understand from this?

Answer 24

We understand that operators are functions, so they`re running code, and coercion is part of that process of calling that function, coercion happens because JS it´s dynamically typed.

Question 25

Explain why this code returns Trueconsole.log( 3 < 2 < 1 );

Answer 25

Thanks to operators precedence and associativity, we now that the “< operator” is called 2 times so it has the same precedence, so associativity comes into place. The associativity is left-to-right.”3 < 2” is called first, and the result is a boolean of “false”. Thanks to coercion, “false” is converted to the number of 0, so “0 < 1” is TRUE

Question 26

When coercion reprensents a problema that might be hard to debug? and why?

Answer 26

When we are comparing two valueswith the “==” operator, and one of the values is not from the same typeThe double equal operator “==” will try to coerce one of the values to the other type

Question 27

How can we solve, the comparision problem with the “==” double equal operator, knowing that coercion could happend

Answer 27

We can use the “===” triple equal operator “strict equality”, that compares if they are the same type and the value. If they are not the same type, it will return FALSE

Question 28

Why this is all falseBoolean(undefined) // falseBoolean(null) // falseBoolean(“”) // false

Answer 28

Because of coercion, all things that imply the lack of existence, they convert to false.

Question 29

Describe one way to use coercion to our advantage?

Answer 29

Using an “if” statement

Question 30

Why the use of an “if” statement, can helps us to use coercion to our advantange?

Answer 30

Because whatever we put inside the parentheses of an if statement, it will attempt to convert or coerce to a Boolean

Question 31

When can we face a problem using an “if” statement and coercion to our advantange…

Answer 31

When we are going to coerce the value of 0, becauseBoolean(0) –> False0 is not lack of existence, maybe it’s a valid value

Question 32

How can we solve the problem using coercion, in an “if” statement, if we know that there is any chance that the value to coerce is going to be a 0?

Answer 32

doing:var a; // it goes to the interner and returns somethingif(a || a === 0) { }Thanks to operator precedence and associativity, we know that it’s going to compare first if “a”, so if a has a value it will coerce to TRUE, either if is 0 and is FALSE, the || operator will do “a === 0”, and result in TRU

Question 33

How can we use coercion if we want to have a default value in a function and we don´t have passed any parameters to it?and when it could be a problem, with what value?

Answer 33

We can use the operator ||name = name || “default name”thanks to operator precedence “||” is going to be run before “=”, and “||” will return the first value that is TRUE, so if name has not existence it means it`s FALSE, then it will return “default name” and will be assigned to “name”We still need to be careful if name = 0;

Question 34

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

Answer 34

A primitivethat is called a propertyAn object that is called a property alsoFunctions that are called methods

Question 35

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

Answer 35

YES

Question 36

How is important to think about an Object as…(When we talk about how it´s an object in memory)

Answer 36

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 37

How can we access those slots in memory, those properties and methods of an object?and how are their names(of the operators)?

Answer 37

With 2 operators:the dot operator . also called member accessthe computed memeber access operator [ ]

Question 38

What does the computed member access operator [ ] ?and help me to remember what an operator is, under the hood?

Answer 38

Remember, an operator is a function.The computed member operator, takes two parameters and it’s associativity is left-to-rightto the left it takes the object, and inside the [ ] it takes the property or method

Question 39

What does the dot . operator do?

Answer 39

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 40

What is the other name of the dot . operator?

Answer 40

It´s also called Member Access

Question 41

Why the dot . operator is called Member Access

Answer 41

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

Question 42

How can we create an object with object literals

Answer 42

using curly braces { }

Question 43

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

Answer 43

It´s treated as one line of code

Question 44

When it gets really powerful to use object literals?

Answer 44

Because we can create objects on the flyFor example, on passing parameters to a function, as an object literal

Question 45

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 45

We can call the greet funciton, and create an object on the flygreet({ firstname:‘Tony’, lastname:‘Garcia’});

Question 46

What “think” the JS engine when itsees:greet({ firstname:‘Tony’, lastname:‘Garcia’});

Answer 46

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 47

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 47

YES

Question 48

What is a Namespace?

Answer 48

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

Question 49

JS have namespaces? and why?

Answer 49

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

Question 50

How can we fake namespaces, for preventing collisions like this one:var greet = “hello!”;var greet = “hola!;console.log(greet) // hola!

Answer 50

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 okayvar english = { greetings: { basic:‘Hello’ }}console.log(english.greetings.basic);

Question 51

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

Answer 51

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 52

What it means JSON, and what is JSON

Answer 52

Javascript object notation.It´s just a string of data

Question 53

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

Answer 53

in quotes “ “

Question 54

JSON is a part of JS?

Answer 54

No

Question 55

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

Answer 55

{“firstname”: “Mary”,“isAProgrammer”: true}

Question 56

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

Answer 56

using the JSON.stringify() method

Question 57

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

Answer 57

using JSON.parse() method

Question 58

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

Answer 58

1) YES2) NO

Question 59

What is the meaning of “first class functions”

Answer 59

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 60

In JS, functions are objects?

Answer 60

YES

Question 61

Does a function object resides in memory?

Answer 61

Yes, it resides in memory

Question 62

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

Answer 62

YEs

Question 63

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

Answer 63

Yes, you can.Because it´s just an object

Question 64

Does function objects has some hidden special properties?

Answer 64

YES

Question 65

What are the hidden properties of a function object?

Answer 65

the code propertyand the name property (it could also be anonymous)

Question 66

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

Answer 66

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 67

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

Answer 67

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

Question 68

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

Answer 68

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

Question 69

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 69

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

Question 70

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

Answer 70

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 71

What is an expression?

Answer 71

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

Question 72

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

Answer 72

a function statement just do worka 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 73

function expressions are hosited?

Answer 73

no, it just hoisted the variable

Question 74

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

Answer 74

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 75

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

Answer 75

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 76

When we pass values “by value” what do we mean:ej:var a = 3;var b = a;

Answer 76

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 77

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

Answer 77

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 78

When we talk about “by value” and “by reference”Which one apply to whicn onePrimitives and objects types

Answer 78

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

Question 79

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

Answer 79

It will point to the Global Object

Question 80

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

Answer 80

It will point to the Global Window Object

Question 81

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

Answer 81

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

Question 82

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 82

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

Question 83

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 83

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” keywordvar 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 84

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 84

It will be poiting to the global object

Question 85

What is an array?

Answer 85

Its a collection of anything, it can holds many things

Question 86

How can we declare an array using array literals

Answer 86

var a = [1, 2, 3];

Question 87

Complete the sentenceBecause JS is …… ….. we can put anything into an array

Answer 87

dynamically typed

Question 88

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

Answer 88

YES

Question 89

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

Answer 89

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 90

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

Answer 90

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

Question 91

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

Answer 91

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

Question 92

How can we make a IIFE immediately function expression?

Answer 92

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 93

What is the purpose of having an IIFE?

Answer 93

To protect our code from other outside codeTo prevent us to put something accidentally in the global object

Question 94

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

Answer 94

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 Johnthat´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 95

Why we can return a function as a value?

Answer 95

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

Question 96

Que es un closure?

Answer 96

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) creasu propio contexto de ejecución.Nos sirve para tener una “factory function” funciones creadoras de funciones.

Question 97

What is a callback function?

Answer 97

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(‘reallydone!’);});

Question 98

What does the bind() method

Answer 98

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 99

what does call()

Answer 99

let me decide what “this” will be, and i can pass arguments to itcall() doesn´t create a new function, it works as if we invoke it

Question 100

what does apply()

Answer 100

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

Question 101

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

Answer 101

call() and apply()For function borrowing, when we want to use a method from one object, on another object!

Question 102

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

Answer 102

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 2function multiply(b) { var a = 2; return a * b;}

Question 103

What means, function currying?

Answer 103

Creating a copy of a function but with some preset parameters

Question 104

To where points “this” in this casefunction asdf() {console.log(this);}

Answer 104

To the global windows object.

Question 105

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 105

Podemos fijarnos como es invocada esa funcion / metodoel 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 106

Describe what is “this”(to where it points) in the following scenarios:1) Inside a method of an object2) Inside a function statement3) Inside a function expression4) An internal function, that it´s located inside a method of an object

Answer 106

This points to:1) The object itself, the object that is calling the method2) global variable window3) global variable window4) points to the global variable( lot of people think this is a bug)

Question 107

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

Answer 107

To have variables inside and secure in a closure

Question 108

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 108

Using a function factory, and returning a functionWhen 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 109

What is the key to understandin closures?Every time you call a function…

Answer 109

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 110

For what are useful the function factories?

Answer 110

To stop passing parameters that could be used as defaultvar greetEnglish = makeGreeting(‘en’) // makeGreeting returns a functiongreetEnglish(‘Bruno’, ‘De Angeli’); // greetEnglish has the returned funciton with the language set by default, tx to closures.

Question 111

How creates a closure, the JS or us?

Answer 111

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

Question 112

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 112

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

Question 113

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

Answer 113

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.