Original subtitles

Alright now

let's take a look at the logical operators. We use these operators

to make decisions based on multiple conditions.

In JavaScript we have three types of logical operators,

logical and logical or and logical not. Let's see

each of these operators in action. So I'm going to start

with the logical and which indicated by

2 ampersands. So here's the basic rule of thumb.

This logical and returns true if both

operands are TRUE. What do I mean by that?

Well, let's do a console.log,

true and true. So we have two operands,

they are both true, so the result of evaluating,

this expression will be true. Let's have a look on the console.

Look, here we get true. Now if either

of these is false, the result will be false, so I'm going to change

this to false, save the changes,

note that we get false on the console, it doesn't matter which one is

false, if I make the other one false, or both of them false, I

still get false. So logical and returns

true if both operands are true. Now you might be asking

what is a real world use case for this operator? Well, let's

imagine we want to build an application for approving loans.

So we want to see if the applicant has high income and

a good credit score, then they will be eligible for loans.

So, I'm going to delete all this,

and declare a couple variables, high income, we're going to

set that to true, and good credit

Score, we're going to send that to true as well.

So here we're dealing with two conditions, we want to make sure that

the applicant has high income, and good credit score.

That's where we use the logical and. So we can declare another

variable, eligibleForLoan

and this is where we use the logical and operator.

So high income and goodCreditScore.

Now, if we log this on the console,

eligible for loan, we should get true, and

here's the result, now let's take a look at the logical or.

So, logical or is indicated by

two vertical lines, and this returns true

if one of the operands

is True. It doesn't matter which one, whether the one on the left,

or the one on the right or both of them, as long as we have one true

operand, the result of this expression will be true. So here's

an example. I'm going to replace this logical and with

logical or, now in this case both operands are true, so the

result of this expression will also be true. Let's have a look. So I'm going to

save the changes to get true, now if I save one of these to

false, we still get true.

It doesn't matter which one is true. As long as we have one operand

in this expression that evalues to true the

result of this expression will also be true. So this is how we use

the logical or. And finally, let's look at

the not operator. That is indicated by

an exclamation mark. So let's imagine that the

applicant is not eligible for loan, you want to consider the

application as refused. So we can declare

another variable applicationRefused

here we use the not operator, we apply

it on eligibleForLoan, so this is

what happens here. If eligible for loan is true, this

not operator will convert that to false. So whatever

we give it, it will give us the opposite, in this case

eligible for loan is true, this will convert that to false,

and applicationRefused will be false. Because if

someone is eligible for a loan, we don't want to refuse their application, right?

So application refused, is always the opposite of

eligibleForLoan, and that's where we used the not operator.

So let's see this in action. I'm going to change both these conditions

to false. So we're dealing with someone who

has low income and a bad credit score, obviously they are not eligible for

a loan, so let's log this on the console,

eligible for loan, and we can also add a label so

I'm going to add a string, eligible, and here we add

comma, then we apply the not operator,

to set the application refused variable, let's do another console

.log, application refused,

and here we log application refused variable.

Now let's see what we get on the console to save the changes

you can see if this applicant is not eligible

because eligible is false, and application refused is

true because it's always the opposite of eligible for loan.