Section 3: Types and Operators

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

undefined

null

boolean

number

string

symbol

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: Null

and 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: Number

Exist 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: String

What 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, +, -, >, <, what is happening?

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 returned

Inside 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 True

console.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 values with the “==” operator, and one of the values is not from the same type

The 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 false

Boolean(undefined) // false

Boolean(null) // false

Boolean(“”) // 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, because

Boolean(0) –> False

0 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 something

if(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;