Day 2

Question 1

The _____ and ______ were introduced in ES6, making them a modern JS syntax. They are a new way of declaring variables.

Answer 1

let and const

Question 2

While the _____ variable is the old way of declaring variables.

Answer 2

var

Question 3

We use _____ keyword to declare variables that can change values later.

Answer 3

let

Question 4

When you change the value of a variable, its technical term is called _________ a value.

Answer 4

Reassigning or mutating

Question 5

We also use let whenever we want to declare ______________. It is a common practice to declare variables with empty values (usually at the top of the file) and then reassign them later.

Answer 5

empty variables

Question 6

On the other hand, we use the _______ keyword to declare variables that are NOT supposed to change at any point in the future. So the values declared with this cannot be changed.

Answer 6

const

Question 7

You will get a _______________, if you attempt to change the value of a variable declared with const.

Answer 7

TypeError

Question 8

In techical terms, variables declared with const are ___________ variable.

Answer 8

immutable

Question 9

True of false: Now the fact that variables created with const are immutable, it also means that we CANNOT declare empty const variables.

Answer 9

True

Question 10

True of false: You can declare empty variable with const.

Answer 10

False - variables declared with const are immutable.

Question 11

Is this valid: const job;

Answer 11

No. You can’t declare an empty variable with const, you need to assign them with an initial value (initializer)

Question 12

Basically, we need an ________ value (or __________) when using const declaration.

Answer 12

Initial or initializer

Question 13

True of false: It is a best practice to always use const by default and let only if you are really sure that the variable needs to change at some point in the future.

Answer 13

True

Question 14

True of false: It is a best practice to have as little variable mutation or variable changes as possible, because changing variables introduces a potential to create bugs.

Answer 14

True

Question 15

Another way to declare variables, but should now be avoided.

Answer 15

var

Question 16

Prior to ES6, _____ is used to create variables.

Answer 16

var

Question 17

At first sight, it works pretty much the same as let.

Answer 17

var

Question 18

True or false: It’s recommended to still use var in modern JavaScript.

Answer 18

False - use let or const instead

Question 19

True or false: You can actually declare a variable without the use of let, const, or var but it’s a bad practice, and you’ll learn more later why.

Answer 19

True

Question 20

This operators perform arithmetic on numbers (literals or variables).

Answer 20

Arithmetic operators

Question 21

True or false: You can log multiple values in console.log(ageJonas, ageSarah)

Answer 21

True

Question 22

True or false: You cannot perform arithmetic operations inside of console.log()

Answer 22

False - you can

Question 23

What is exponentiation operator looked like?

Answer 23

**

Question 24

True or false: We can use the plus operator to join or concatenate strings.

Answer 24

True

Question 25

Given that the variables are declared. Is this valid: console.log(firstName + ‘ ‘ + lastName);

Answer 25

Valid

Question 26

Operator used to assign values to a variable

Answer 26

Assignment operator

Question 27

This operator adds the value of the right operand to a variable and assigns the result to the variable.

Answer 27

addition assignment operator (+=)

Question 28

This operator increments (adds one to) its operand and returns the value before or after the increment, depending on where the operator is placed.

Answer 28

increment operator (++)

Question 29

We use ___________ operators to produce boolean values.

Answer 29

comparison (and of course logical)

Question 30

True or false: The Console tab in developer tools has access to all variables in present in the browser tab.

Answer 30

True

Question 31

JavaScript has a well-defined order of operator ___________. Basically, the order in which operators are executed.

Answer 31

precedence

Question 32

True or false: Comparison operators has lower precedence than arithmetic operators. This means arithmetic operators executes first than comparison operators.

Answer 32

True

Question 33

True or false: Most of the operators execute from left to right, but some execute from right to left like assignment operator.

Answer 33

True

Question 34

True or false: You can declare two empty values: let x, y;

Answer 34

True

Question 35

Give a type of operator that has right to left associativity

Answer 35

Assignment operator or exponential

Question 36

What will be the value of x and y: x = y = 25 - 10 - 5;

Answer 36

10 and 10

Question 37

Which has the highest order of precedence?

Answer 37

Grouping

Question 38

What is the result: const ageAverage = 20 + 20 / 2;

Answer 38

30

Question 39

What is the result: const ageAverage = (20 + 20) / 2;

Answer 39

20

Question 40

It’s easier to building strings using _______________.

Answer 40

Template literal

Question 41

Starting ES6, there’s a much easier way to concatenate strings with __________.

Answer 41

Template literal

Question 42

We use ____________ to write template literals, and we can wrap variables inside of __________.

Answer 42

Backticks (``) and interpolation ${}

Question 43

True or false: You can also write regular strings using template literals.

Answer 43

True

Question 44

You can write multi line strings much easier with ______________.

Answer 44

template literals

Question 45

Use the_______________ to specify a block (code inside curly braces) to be executed if a condition is true.

Answer 45

if statement

Question 46

The ________________ is executed when if statement or else if statement are not executed.

Answer 46

else statement

Question 47

The if else statement is called a _________________. They are commands that enable a program to “take decisions”, following one path or another.

Answer 47

control structure

Question 48

True or false: It’s important to remember that any variables we declare inside of a code block cannot be accessible outside of the code block.

Answer 48

True

Question 49

When we manually convert from one type to another.

Answer 49

Type conversion

Question 50

To convert a string to a number we use the ____________ function.

Answer 50

Number()

Question 51

What happens if we try to use Number() function but the string does not contain number? What will it return?

Answer 51

NaN

Question 52

JS will return _______ when an operators that involves numbers failed to produce a new number. It actually means ______________, not ‘not a number’.

Answer 52

NaN, invalid number

Question 53

Now to convert a number to a string we use _____________ function.

Answer 53

String()

Question 54

When JavaScript automatically converts types behind the scenes for us.

Answer 54

Type coercion

Question 55

True or false: We rarely do type convertions since JS automatically converts types for us.

Answer 55

True

Question 56

True or false: Basically, type coercion happens whenever an operator is dealing with two values that have different types.

Answer 56

True

Question 57

True or false: The plus operator will convert strings to numbers.

Answer 57

False - The plus operator will convert numbers to strings.

Question 58

True or false: The minus operator triggers the opposite conversion, it instead converts strings to numbers.

Answer 58

True

Question 59

True or false: Other arithmetic operators like multiplication and division will convert string to a number.

Answer 59

True

Question 60

True or false: When we compare strings (that looked like numbers) using logical operators, it will result to Error.

Answer 60

False - When comparing the strings it will be converted to numbers automatically.

Question 61

The _______ values are values that are not exactly false, but will become false when we try to convert them into a Boolean.

Answer 61

falsy

Question 62

In JS, there are only five falsy values. These are:

Answer 62

0, empty string, undefined, NaN, null

Question 63

True or false: Everything else, are considered truthy values.

Answer 63

True

Question 64

We use the _______________function to find out if an expression (or a variable) is truthy or falsy:

Answer 64

Boolean()

Question 65

When does JS do type coercion to Booleans?

Answer 65

When you use a value (other than Boolean) as condition to your if statements. It will convert them to either truthy or falsy value.

Question 66

What are the two types of equality operators?

Answer 66

Strict equality operator (===) and Loose equality operator (==)

Question 67

True or false: Whenever our if block only has one line of code to execute, the use of curly braces is unnecessary.

Answer 67

True

Question 68

The strict equality operator is strict because it does not perform ______________. It only returns true if both values are exactly the same and its type is also the same.

Answer 68

type coercion

Question 69

What is the result: console.log(’18’ === 18);

Answer 69

false

Question 70

On the other hand, the ___________________ operator does type coercion.

Answer 70

loose equality operator (==)

Question 71

What is the result: console.log(’18’ == 18);

Answer 71

true

Question 72

What is strict inequality operator syntax looks like?

Answer 72

!==

Question 73

The ________________ is a branch of computer science, which uses true and false values to solve complex logical problems.

Answer 73

Boolean logic

Question 74

We will only learn the three most basic logical operators which are the ______ operators

Answer 74

AND, OR, and NOT

Question 75

Returns true only if two values or more values are true. Basically, it will only return true if all are true.

Answer 75

AND

Question 76

Returns true even if there is only one true.

Answer 76

OR

Question 77

It does not combine multiple values. Instead, this operator only acts on one Boolean value and basically inverts it.

Answer 77

NOT

Question 78

True or false: The NOT operator has lower precedence over the AND and OR operator.

Answer 78

False - The NOT operator has higher precedence over the AND and OR operator.

Question 79

What is the syntax of AND operator?

Answer 79

&&

Question 80

What is the syntax of OR operator?

Answer 80

||

Question 81

What is the syntax of NOT operator?

Answer 81

!

Question 82

An alternative way of writing complicated if else statements

Answer 82

switch statement

Question 83

Write down a boilerplate for a switch statement.

Answer 83

switch(), then curly brackets, inside of it is case:, and should have break;. It also contains a default:

Question 84

True or false: With switch statements, we can run the same code for multiple cases.

Answer 84

True

Question 85

True or false: We don’t need to put break; after every case.

Answer 85

False - We need to put break; after every case.

Question 86

In a switch statement, the __________ will execute if none of the cases are executed. Like else.

Answer 86

default

Question 87

True or false: If you omit the break; the code simply continues executing until it sees a break;.

Answer 87

True

Question 88

An ____________ is a piece of code that produces a value.

Answer 88

expression

Question 89

A bigger piece of code that is executed and which does not produce a value on itself.

Answer 89

statements

Question 90

Term for ‘sequence of actions’

Answer 90

statements

Question 91

In a template literal, we can only put expressions not _____________.

Answer 91

statements

Question 92

What do we call this ${}

Answer 92

Interpolation

Question 93

We already saw two ways of writing conditionals. The regular if else statement and switch statement. But there is another one, and that is the _________________.

Answer 93

conditional (ternary) operator

Question 94

Theconditional (ternary) operatoris the only JavaScript operator that takes three operands, which are:

Answer 94

The condition, followed by a question mark (?), then an expression to execute if the condition istruthyfollowed by a colon (:), and finally the expression to execute if the condition isfalsy.

Question 95

True or false: The conditional operator allows us to write something similar to an if else statement but all in one line.

Answer 95

True

Question 96

True or false: It’s called ternary operator because it has three parts: the condition, the code executed for if part, and then the code executed for the else part.

Answer 96

True

Question 97

True or false: Now the conditional operator is in fact an operator, and an operator always produces a value. So in other words an operator is an expression, right?

Answer 97

True

Question 98

True or false: The ternary operator does not replace the if else statement, we still need if else statement when we’re writing code that needs more option (else if). The ternary operator is only good when we just need a quick decision.

Answer 98

True

Question 99

Can you put conditional ternary operator inside the interpolation of a template literal?

Answer 99

Yes. It’s valid.

Question 100

Netscape Navigator, a dominant browser at its time, hired a guy named __________ to create a very first version of JS.

Answer 100

Brendan Eich

Question 101

Brendan Eich creates the very first version of JS in just ___ days. It was called _______, but already had many fundamental features of modern JavaScript!

Answer 101

10, Mocha

Question 102

Mocha changes to __________ and then to JavaScript, in order to attract Java developers. However, JavaScript has almost nothing to do with Java.

Answer 102

LiveScript

Question 103

Microsoft launches IE, then copied JS from Netscape and called it _______.

Answer 103

JScript

Question 104

Year when JS was invented

Answer 104

1995

Question 105

ES6 is also called _______.

Answer 105

ES2015

Question 106

They need to standardize the language, __________ releases ECMAScript 1 (ES1), the first official standard for JS (ECMAScript is the standard, JS is the language in practice)

Answer 106

ECMA

Question 107

Year when ES5 is introduced.

Answer 107

2009

Question 108

True or false: Code back all the way from 1997 will still work on modern browsers. This means that modern browsers are backwards compatible.

Answer 108

True

Question 109

The concept of _______________ means that there is almost never anything removed from the language, but only added in new versions. Not really new versions, just incremental updates (releases)

Answer 109

Do not break the web

Question 110

JavaScript is not ____________ compatible simply because there is no way browsers from today can understand the updates that is coming from the future.

Answer 110

forwards

Question 111

True or false: It’s still important to understand old JS syntax like ES5.

Answer 111

True - since some older code bases are written in ES5.