Types and Grammar

Question 1

What is a type?

Answer 1

A type is an intrinsic build in set of characteristics that uniquely distinguishes the behavior

Question 2

Javascripts built in types (7)

Answer 2

null
undefined
boolean
number
string
object
symbol

Question 3

Except for objects, all JS types are called:

Answer 3

Primitives

Question 4

Function is what type?

Answer 4

object. Specifically a “callable object”

Question 5

function.length returns

Answer 5

the number of formal parameters is it declared with

Question 6

Array is what type?

Answer 6

A subtype of object

Question 7

typeof [“d”,”a”]

Answer 7

object

Question 8

var a;

typeof a

Answer 8

undefined

Question 9

undefined vs undeclared

Answer 9

Undefined has been defined in accessible scope but not defined. Undeclared hasn’t been declared.

Question 10

var a = []
a["13"] = "hello";
What will happen?

Answer 10

a will be populated with undefined until a[13] which is hello

Question 11

mutability of strings

Answer 11

immutable

Question 12

mutability of arrays

Answer 12

mutable

Question 13

with a decimal value of eg 0.42, is the 0 optional?

Answer 13

yes

Question 14

With a decimal value of 42.30, is the 0 optional?

Answer 14

yes

Question 15

Why is 0.1 + 0.2 == 0.3 false?

Answer 15

Binary floating point numbers are not exact. It’s actually like .300000000004. This is like a number epsilon.

Question 16

Whats the best way to compare float calculations?

Answer 16

Use a tiny rounding error. See that a - b < Number.EPSILON

Question 17

Can you create

var undefined in unstrict more?

Answer 17

yes

Question 18

NaN is a type of

Answer 18

Number. 
eg var a = 1+"foo"
typeof a === "number" >> true

Question 19

How to check if a value is NaN and why?

Answer 19

isNaN(a)

We have to do this because NaN is a type of number

Question 20

downfalls with isNaN

Answer 20

Literally checks if it is NaN. Strings return true for example instead of whether it is a NaN subtype

Question 21

What can you do to check if it is type NaN?

Answer 21

var a = 3/"hello"
Number.isNaN(a)

Question 22

1/0 is

Answer 22

infinity