Javascript Essentials

Question 1

Function Overloading

Answer 1

the ability to create multiple functions of the same name with different implementations

Question 2

whitespace

Answer 2

invisible characters that create literal ‘space’ in your written code

Question 3

Immediately Invoked Function Expressions

Answer 3

a JS expression that runs as soon as it’s defined

Question 4

Array

Answer 4

a variable that holds many values insdie of it []

Question 5

arguments

Answer 5

the parameters that you pass to a function

Question 6

mutate

Answer 6

to change a value

Question 7

immutable

Answer 7

cannot be changed

Question 8

JSON

Answer 8

Javascript Object Notation

Question 9

First Class Functions

Answer 9

everything you can do with other types you can do with functions, assign them to variables, pass them around, create them on the fly. function names can be anonymous. Functions are an object whose code happens to be the properties on that object.

First Class Functions = Functional Programming

Question 10

Function expression

Answer 10

a unit of code that results in a value. It doesn’t have to save a variable. Usually created on the fly.

Question 11

function statement

Answer 11

a function that just ‘does work’

Question 12

Namespace

Answer 12

a container for variables and functions, typically to keep variables and functions with the same name seperate.

Question 13

Primitive Property

Answer 13

number, boolean, string

Question 14

Object Property

Answer 14

Object within Object

Question 15

Function Method

Answer 15

a function that is connected to an object

Question 16

Operator

Answer 16

a special function that is syntactically (written) differently.

Question 17

Precedence

Answer 17

which operator gets called first (PEMDAS)

Question 18

Associativity

Answer 18

what direction operator functions get called in L->R R->L

Question 19

coercion

Answer 19

converting a value from one type to another

Question 20

array.filter()

Answer 20

creates a new array with all elements that pass the test implemented by the provided function.

Question 21

array.map()

Answer 21

creates a new array with the results of calling a provided function on every element in the calling array

Question 22

array.reduce()

Answer 22

method executes a reducer function (that you provide) on each element of the array, resulting in a single output value. The reducer function takes four arguments:

Accumulator (acc)
Current Value (cur)
Current Index (idx)
Source Array (src)

Your reducer function’s returned value is assigned to the accumulator, whose value is remembered across each iteration throughout the array and ultimately becomes the final, single resulting value.

Question 23

trim

Answer 23

method removes whitespace (spaces, newlines, tabs, and similar) from the start and end of a string

Question 24

padstart()

Answer 24

The padStart() method pads the current string with another string (multiple times, if needed) until the resulting string reaches the given length. The padding is applied from the start (left) of the current string.

Question 25

string.length()

Answer 25

accessing individual characters in a string looks like accessing array elements. It returns count of total number of characters. The length of java string is same as the unicode code units of the string.

Question 26

rest parameters (…Args)

Answer 26

it can useful for a function to accept any number of arguments. The rest parameter syntax allows us to represent an indefinite number of arguments as an array.

Question 27

array.indexOf()

Answer 27

method searches through the array from the start to the end and returns the index at which the value was found, or -1 if not found.

Question 28

array.slice()

Answer 28

takes the start and ending indexes and returns an array that has only the elements between them. The slice() method returns a shallow copy of a portion of an array into a new array object selected from begin to end (end not included). The original array will not be modified.

Question 29

array.concat()

Answer 29

The concat() method is used to merge two or more arrays. This method does not change the existing arrays, but instead returns a new array.

Question 30

array.splice()

Answer 30

The splice() method changes the contents of an array by removing or replacing existing elements and/or adding new elements

Question 31

indexOf()

Answer 31

The indexOf() method returns the first index at which a given element can be found in the array, or -1 if it is not present.

Question 32

lastIndexOf()

Answer 32

The lastIndexOf() method returns the index within the calling String object of the last occurrence of the specified value, searching backwards from fromIndex. Returns -1 if the value is not found.

searchValue: A string representing the value to search for. If searchValue is an empty string, then fromIndex is returned.

Takes an optional second argument that indicates where to start searching.

Question 33

array.push() & array.pop()

Answer 33

add and remove elements at the end of an array.

Question 34

array.shift() & array.unshift()

Answer 34

add and remove elements at the start of an array.

Question 35

array.includes()

Answer 35

The includes() method determines whether an array includes a certain value among its entries, returning true or false as appropriate.

Question 36

==

Answer 36

compares by identity, it will produce true only if both objects are precisely the same value.

Question 37

stack

Answer 37

a data structure that allows you to push values to it, and remove them as well.

Question 38

properties

Answer 38

all .js values have properties, exception is null and undefined

Question 39

delete

Answer 39

operator unary, when applied to an object property, will remove the named property from the object

Question 40

object

Answer 40

arbitrary collections of properties

Question 41

pure function

Answer 41

a specific kind of value producing function that not only has no side effects but doesn’t rely on side effects from other code. -> doesn’t read global bindings whose value might change.

Question 42

recursion

Answer 42

a function that calls itself until a base case is reached and some value is returned.

Question 43

closure

Answer 43

being able to reference a specific instance of a global binding in an enclosing space, a function that references bindings from local scopes around it.

Question 44

function definition

Answer 44

a regular binding where the value of the binding is a function.

Question 45

local binding

Answer 45

created for function parameters or declared inside a function, can be referenced only by that function.

Question 46

enumerable

Answer 46

any property you add to an object (not those that are inherited) can be iterated over.

Question 47

pseudoclassical instantiation

Answer 47

prototype in JS is just a property on a function that points to an object, or a property that every js function has that points to an object

Question 48

object.create

Answer 48

allows you to create an object that will delegate to another object on failed lookups. consults another object to see if that object has the property.

Question 49

prototype

Answer 49

every function in Javascript has a prototype property that references an object, allows us to share methods across all instances of a function.

Question 50

functional instantiation

Answer 50

encapsulate logic inside a function that can be invoked when creating new instances of an object. Called a constructor function, since it is possible for constructing an object.

Question 51

dynamic typing

Answer 51

you don’t tell the engine what type of data a variable holds, it figures it out while your code is running.

Question 52

Syntax Parser

Answer 52

a program that reads your code and determines what it does and if its grammer is valid.

Question 53

Class

Answer 53

Classes are in fact “special functions”, and just as you can define function expressions and function declarations, the class syntax has two components: class expressions and class declarations.

Question 54

constructor method

Answer 54

A JavaScript class is a type of function. Classes are declared with the class keyword. The constructor method is a special method for creating and initializing an object created with a class. There can only be one special method with the name “constructor” in a class. A SyntaxError will be thrown if the class contains more than one occurrence of a constructor method.

Question 55

null

Answer 55

intentionally having no value

Question 56

undefined

Answer 56

a declared variable that hasn’t been assigned a value yet

Question 57

boolean

Answer 57

true or false

Question 58

Symbol

Answer 58

a unique value that’s not equal to any other value. Note, this is an ES6 feature that never really took off, so don’t worry about it for now.

Question 59

string

Answer 59

a series of characters (letters, numbers, spaces, symbols, etc.) wrapped in quotes

Question 60

Object

Answer 60

Objects in JavaScript, just as in many other programming languages, can be compared to objects in real life. Objects are standalone entities, with properties stored in key/value pairs. Compare it with a person, for example. A person is an object, with properties. A person has a race, a date of birth, a weight, a height, an eye color, etc. The same way, JavaScript objects can have properties, which define their characteristics.

Question 61

array

Answer 61

Used to store multiple values in a single variable. Similar to a list. Technically, arrays are objects in JavaScript, but we’ll dive into that more in second half of the pre-course.

Question 62

escape sequences

Answer 62

ways of formatting characters in strings.
Anytime JavaScript sees a () inside of a string, it knows that the following character has a special meaning. Here is a list of some of the most common escape sequences:

\' => single quote
\" => double quote
\\ => backslash
\n => newline
\r => carriage return
\t => tab
\b => backspace
\f => form feed

Question 63

template literals

Answer 63

Template literals are a special type of string that make creating complex strings so much easier. Template literals are created by surrounding text between opening and closing backticks (``). Inside a template literal, you’re able to refer to variables or execute code by using ${}

Question 64

The exponentiation operator (**)

Answer 64

The exponentiation operator (**) raises the first number to the power of the second number.

Question 65

== and !=

Answer 65

is loosely equal/not equal to

Question 66

=== and !==

Answer 66

is strictly equal/not equal to

Question 67

parseInt()

Answer 67

The parseInt() function parses a string argument and returns an integer of the specified radix (the base in mathematical numeral systems).

Question 68

hoisting

Answer 68

variable and function declarations are put into memory during the compile phase, but stay exactly where you typed them in your code.

Question 69

free variable

Answer 69

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

Question 70

string.substring()

Answer 70

The substring() method returns the part of the string between the start and to but not including the end indexes, or to the end of the string if only one index given.

Question 71

array.slice(i, i)

Answer 71

method returns a shallow portion of an array object into a new array object from beginning endex to ending index, or to end of array if index not provided.

Question 72

array.unshift(things to add)

Answer 72

The unshift() method adds one or more elements to the beginning of an array and returns the new length of the array.