JS Fundamentals

Question 1

ES5 supports the following data types

Answer 1

number, string, Boolean and undefined

Question 2

ES5 uses ____ to declare a variable

Answer 2

var

Question 3

ES5 cannot import ____ into another file

Answer 3

JSX

Question 4

ES5 uses the _____ module to include a react module or component

Answer 4

RequireJS module

ES5 uses the RequireJS module to include a react module or component

Question 5

ES5 uses ____ syntax

Answer 5

ES5 uses function(){} syntax

Question 6

ES5 props are…

Answer 6

ES5 props are implicitly defined and we add this to functions

Question 7

ES5 doesn’t require a ____ to render in the web

Answer 7

a transpiler like Babel

Question 8

ES6 supports the following data types:

Answer 8

number, string, boolean, undefined and Symbol

Question 9

ES6 uses the following to declare a variable

Answer 9

var, let and const

Question 10

ES6 can import a ____ file to another file

Answer 10

JSX

ES6 can import a JSX file to another file

Question 11

ES6 uses the ____ to include a react module or component

Answer 11

import module

ES6 uses the import module to include a react module or component

Question 12

ES6 uses ____ function syntax

Answer 12

arrow function

ES6 uses arrow function syntax

Question 13

ES6 props are passed ____ though a ____

We _____ bind ____ to ____ in the ____

Answer 13

ES6 props are passed EXPLICITLY though a CONSTRUCTOR

We EXPLICITLY bind this to functions in the constructor

Question 14

ES6 requires a ____ like babel

Answer 14

ES6 requires a transpiler like babel

Question 15

What are the different primitive data types in JS?

Answer 15

string, number, BigInt, Boolean, undefined, null, Symbol

Question 16

What are the different non-primitive data types in JS?

Answer 16

stores multiple and complex values

Question 17

String

Answer 17

Can be represented using a single or double quote

Question 18

Number

Answer 18

Can be written with or without decimals

Question 19

BigInt

Answer 19

Stores numbers about the limitation of Number type

Question 20

boolean

Answer 20

only has two values true or false

Question 21

undefined

Answer 21

when a variable is declared but not assigned

Question 22

null

Answer 22

a non-existent or invalid value

Question 23

Symbol

Answer 23

ES6 data type that stores anonymous and unique property keys

Can create a global Symbol by using the methods Symbol.for() or Symbol.keyFor()

Question 24

Object

Answer 24

can store data in key/value pairs

can store arrays

can store functions

Question 25

hoisting

Answer 25

default behavior of javascript where all variable and function declarations are moved on top.

Question 26

difference between == and === operators

Answer 26

`==` compares values `===` compares value and types

Question 27

implicit type coercion

Answer 27

automatic conversion of value from one data type to another

Question 28

types of coercions

Answer 28

string, boolean, logical, equality

Question 29

string coercion

Answer 29

takes place using the + operator. When a number is added to a string, the return value is always a string type because JS converts the number to a string type before performing the operation ``` var x = 3 var y = "3" x + y // Returns "33" ```

Question 30

boolean coercion

Answer 30

occurs in logical operators, ternary operators, if statements and loop checks

Question 31

equality coercion

Answer 31

takes place when using == operator because == compares values and not types

Question 32

is JS statically typed or dynamically typed

Answer 32

Dynamically typed. the type of a variable is checked during run-time in contrast to a statically typed language, where the type of a variable is checked during compile-time

Question 33

characteristics of static typing

Answer 33

variables have types values have types variables cannot change type

Question 34

characteristics of dynamic typing

Answer 34

variables have no types values have types variables change type dramatically (ie type coercion)

Question 35

Immediately Invoked Function (IIFE, pronounced IFFY)

Answer 35

a function that runs as soon as it is defined ``` (function(){ // do something })() ```

Question 36

Higher Order Functions

Answer 36

Functions that operate on other functions by taking a function as an argument or returning a function ``` function higherOrder(fn) { fn() } higherOrder(function() { console.log("Hello world") }) ```

Question 37

this

Answer 37

the object that is a property of a function

Question 38

call()

Answer 38

method used to call a function ``` function doSomething(){ console.log("hi") } doSomething.call() ```

Question 39

apply()

Answer 39

method used to call a function. The difference is that apply takes arguments as an array ``` function sendMessage(message) { return this.name + "is" + message } var person4 = { name: "John" } sendMessage.apply(person4, ["welcome"]) ```

Question 40

bind()

Answer 40

returns a new function where this is bound to the owner object, which is provided as the parameter

Question 41

currying

Answer 41

``` a function that accepts arguments that are transformed into functions ``` // Noncurried version const add (a,b,c) => {return a + b + c } console.log(add(2,3,5)) // 10 ``` ``` // Curried version const addCurry = (a) => { return (b) => { return (c) => { return a + b + c } } } console.log(addCurry(2)(3)(5)) // 10 ``` ```

Question 42

three types of scopes in JS:

Answer 42

- global - local or function - block scope

Question 43

global scope

Answer 43

code that’s accessible from anywhere inside the code

Question 44

function scope

Answer 44

code that’s accessible from anywhere inside the function

Question 45

block scope

Answer 45

variables declared inside of a block ( such as {})

Question 46

Object prototypes

Answer 46

All objects inherit properties from a prototype. | I.e, (Date, Math, Array, etc)

Question 47

callback

Answer 47

functions that are used as an argument to another function

Question 48

memoization

Answer 48

a form of caching where the return value is cached based on the parameters. If the parameter is not changed, the cached value is returned

Question 49

recursion

Answer 49

when a function repeatedly calls itself until it arrives at a result

Question 50

rest parameter

Answer 50

indicates there’s an unknown number of parameters in an argument. Must be used as the last parameter of an argument

Question 51

spread operator

Answer 51

used to spread arrays or objects

Question 52

JS classes

Answer 52

syntactic sugar for constructor functions Before we would ```jsx function Student(name){ this.name=name } ``` Now ```jsx class Student { constructor(name) { this.name = name } } ```

Question 53

temporal dead zone

Answer 53

the state where variables are unreachable at the time they are called or used ```jsx x = 23 // Gives reference error let x; ```