Boolean Logic

True, False, and Beyond

Boolean Logic

• Everything starts with the idea that a statement is either True or False

• Then we can combine those initial statements to create more complex statements that also evaluate to True or False

Comparison Operators

Assuming x = 5 

Equality Operators

== vs. ===

var x = 99;

x == "99"  //true

x === "99" //false


var y = null;

y == undefined //true

y === undefined //false

"==" performs type coercion, while "===" does not

A Few Interesting Cases

true == "1"          //true

0 == false           //true

null == undefined    //true

NaN == NaN           //false

Logical Operators

AND, OR, and NOT

Assuming x = 5 and y = 9

Exercise 1

var x = 10;
var y = "a"

y === "b" || x >= 10

Exercise 2

var x = 3;
var y = 8;

!(x == "3" || x === y) && !(y != 8 && x <= y)

Truthy and Falsy Values

Values that aren't actually true or false, are still inherently "truthy" or "falsey" when evaluated in a boolean context

!"Hello World"

!""

!null

!0

!-1

!NaN

Try These Examples:

• false
• 0
• ""
• null
• undefined
• NaN 

Everything Else Is Truthy

Truthy and Falsy Values

Falsy Values:

Exercise 3

var str = ""
var msg = "haha!"
var isFunny = "false"

!(( str || msg ) && isFunny)