Ultimate JavaScript Mastery - Part 1

Question 1

What is JavaScript?

Answer 1

A programming language written to be executed within the browser

Question 2

What can you do with JavaScript?

Answer 2

Modern JavaScript can also be used as a server side language as well as front end

Question 3

Where does JavaScript code run?

Answer 3

Originally meant to run only in the browser, but can now be run outside the browser using node

Question 4

Describe the difference between JavaScript and ECMAScript

Answer 4

ECMAScript is simply the standard for which JavaScript, a programming language, is written

Question 5

Where should you place your tag within the browser?

Answer 5

The tag should be written at the end of the body section.

Question 6

What is a statement?

Answer 6

A piece of code that expresses actions to be carried out.

Question 7

Write a script tag

Question 8

What are the data types in JavaScript?

Answer 8

Primitive (Value) Types and Data Types

Question 9

Name the Primitive (Value) Types

Answer 9

String
Number
Boolean
undefined
null

Question 10

Describe Dynamic Typing

Answer 10

JavaScript is a Dynamic Programmming language because variable types can be changed

Question 11

Name the Reference Types

Answer 11

Object
Array
Function

Question 12

What is an object?

Answer 12

A piece of code that stores data via key/value pairs. The keys are known as the properties of the object.

Question 13

A key in an object is also known as what?

Answer 13

Property

Question 14

What are the two ways to access properties within an object?

Answer 14

Dot Notation
ex. person.name = “Kevin”

Bracket Notation
ex. person[‘name] = “Kevin”

Question 15

What are the names of the JavaScript operators?

Answer 15

Arithmetic - takes two operands and produces a new value (+, -, *, /, %, ++, –)

Assignment - assigns a value to a variable (=, +=)

Comparison - A comparison between to expressons that returns a boolean value such as ‘true’ or ‘false’ (>, >=,

Question 16

Give an example of a ternary (conditional) operator

Answer 16

A ternary operator can evaluate an expression and provide two an option if it is true, and an option if false
ex if(age >=21 ? "Old Enough" : "Too Young")

Question 17

What are “falsy” values?

Answer 17

Any expression that evaluates to any of the following will return false.

undefined
null
0
false
""
NaN

Question 18

What is an advantage of using non the logical “or” ( || ) operator with non boolean values?

Answer 18

Using the logical “or” ( || ) with non boolean values will allow you to set default values. For example, if something doesn’t exist, you can have a default value set. For example, If a user hasn’t signed in, you can set mount a default component such as the login

Question 19

What are the 2 conditional statements?

Answer 19

If...else
if(condition) {
  statement
} else if {
  statement
} else {
  statement
}

switch..case
let name = "Kevin"
switch (name) {
  case "Kevin" : console.log("Hello, Kevin");
  break;

case “Preye” : console.log(“Hello, Preye”);
break;

default: console.log(“Hello, guest”)
}

Question 20

Describe the difference between “==” and “===” operators

Answer 20

The “===” operators evalueates both value and type, whereas “==” evaluates just value.

Question 21

What are the 5 kinds of Loops?

Answer 21

For
While
Do…While
For…of

Question 22

What is the anatomy of a for loop?

Answer 22

The for loop requires 3 statements within the parenthesis

for (let i = 0; i <= arr.length; i++) {
  console.log("Hello World")
}
for (initalExpression; condition; incrementExpression) {
  statement
}

Question 23

How is a while loop different from the for loop?

Answer 23

Within a for loop, the loop variable (i) is apart of the loop itself. The while loop, however, has to be declared outside of the loop.

let i = 0;
while(i<=arr.length) {
 console.log(i);
 i++
}

Question 24

Construct a “do…while” loop

Answer 24

let i = 0
do {
  if (i % 2 !== 0) console.log(i);
  i++;
} while (i < = 5);

Question 25

Describe a for…in loop.

Answer 25

A for…in loop is meant to iterate through an object using the syntax
for(let key in fruit )
Fruit is the object being iterated through and key is the current key iteration
Fruit accesses the key and fruit[key] accesses the value

Question 26

Describe a for…of loop

Answer 26

A for…of loop is meant to iterate through an array using the syntax
for(let el in array )

Question 27

Describe OOP

Answer 27

Object-Oriented Programming

Where a program is a collection of objects that talk to each other to perform so sort of functionality

Question 28

What is a javaScript method?

Answer 28

A function within an object

Question 29

Give an example of a factory function.

Answer 29

Factory functions are functions that allow parameters with the purpose of creating objects. 
function foo(firstName, lastName) {
  return {
     firstName,
     lastName,
     fullName() {
       console.log(`${firstName} + ${lastName}`)
     }
   }
}

Question 30

Describe a Constructor function

Answer 30

A contructor function is a function that creates an object. The properties and methods within the object use the “this” keyword.

When creating an object, you should use the “new” keyword. For example.

const Kevin = new Person(param, param2)

Question 31

Describe Value vs. Reference Types

Answer 31

Value types are copied and have no connection to the origin of the value, so if the original variable is changed, the copy isn’t effected. I call them “Simple Values”
(Number, strings, Booleans, Symbols, undefined, null)

Reference values are not copied, they are referenced somewhere in memory, so if the value of the initial variable is changed, it is also changed in any variable referencing the original variable.
Complex values.
(Objects, functions, arrays)

Question 32

What is the shorthand for enumerating through arrays/objects?

Answer 32

Arrays
for (let el of arr)

Objects
for (let key of obj)

Question 33

Describe the two modern way to clone an object.

Answer 33

const newObj = Object.assign({}, circle)
The first parameter passed in is the new object. The 2nd parameter, circle is the object that is to be cloned. Additional properties can also be assigned

We can also use the spread operator
const newObj = {...circle}

Question 34

Name 5 wasy to create a date object

Answer 34

let today = new Date()
let birthday = new Date('November 17, 1984 03:24:00')
let birthday = new Date(1984, 10, 17, 3, 24, 0)

Question 35

Name 7 common Math Methods

Answer 35

Math.PI
Ratio of the a circle’s circumference to its diameter; approximately 3.14159.

Math.abs(x)
Returns the absolute value of x.

Math.ceil(x)
Returns the smallest integer greater than or equal to x.

Math.floor(x)
Returns the largest integer less than or equal to x.

Math.max([x[, y[, …]]])
Returns the largest of zero or more numbers.

Math.min([x[, y[, …]]])
Returns the smallest of zero or more numbers.

Math.random()
Returns a pseudo-random number between 0 and 1.

Math.round(x)
Returns the value of the number x rounded to the nearest integer.

Math.sign(x)
Returns the sign of the x, indicating whether x is positive, negative, or zero.

Question 36

Array methods to master

Answer 36

.fill
.find
.filter
.map
.includes
.reduce
.sort
.every

Question 37

What is the difference between a function declaration and a function expression

Answer 37

A functions declaration is written explicitly as a function whereas a function expression is a function stored within a variable.

Question 38

Describe Hoisting

Answer 38

JacaSCript moves all function declarations (functions not save in a variable) to the top of the file.

Question 39

Describe Getters

Answer 39

Where a method is used within an object, we can’t access the returned value of the method by using obj.key. In order to do this, we need to write the keyword get before the function. This allows you to access the value with dot notation.

Question 40

Describe Setters

Answer 40

Setters allows you to change and save the values of of a method by using set before calling the function

Question 41

What is ‘defensive programming’?

Answer 41

Adding error handling at the beginning of a function to make certain that the logic can be performed. This can mean making sure the the input is the correct type, length, etc and returning a ‘throw new Error(‘Value is incorrect’)’. Try and catch blocks

Question 42

What is the difference between let and var?

Answer 42

Var is function scoped and let is block scoped. Var is accesible outside of a block which causes bugs as it can be altered.

Question 43

Explain the “this” keyword

Answer 43

This refers to the object that is executing the current function. For example, if the function is part of an object (method), then ‘this’ refers to the object. If the function is. a standalone, then this refers to the global object.

When using the constructor function and the operator new, a new empty object is referenced.

Arrow functions allow you to reference the object direcctly without using “.bind( )”

Question 44

Describe the rest operatorand its use.

Answer 44

The rest operator is used when multiple parameters are passed into a function
ex. function sum(…numbers) {

}

The rest operator converts the param into an array, which means, if an array is passed into the function, it will result in an array of arrays