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7: How to Create Variables in JavaScript | JavaScript Tutorial | Learn JavaScript | mmtuts



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how is it going everyone

and welcome back to our next episode

in how to create variables using java script

variable is something that we use often inside java script

we actually use it all the time

and in this example here we are gonna show example how variables work

so you can see how use it inside java script

as you see from here

we have index page open in the right side

and in the left side i have a browser open in the command console

or the developer tool open in the bottom here

now what i'm going to do is going ahead and right

some java script code i'm gonna say i want to

console dot log

which is going to send some kind of information

to the command console inside the browser right no

what to say ten

plus twenty

you guys can see we get thirty inside console

that takes exact same thing if we go inside the console

and write ten plus twenty

we get the same result

this is how can actually we write inside the console from inside out

document inside the index page

now a variable is a type of a container that we've use inside the

java script in order to store data inside of

so right now what if we go inside my code here

i could actually go ahead and create a variable

or declare a variable which we called

by using a keyword called var

now the var keyword says that we now declare the

variable then we need to name it something

when it comes to naming variable as you can name it any kind of name you want

this just a couple of things you need to keep in in mind

when you name this variables first of all you can start with a

number and second of all capitalized letters

and non capitalized letters

do actually matter

so want to create variable called A

semicolon and then create a variable called

capitalized A these two are separate things

and separate variables and they are not the same thing

now to create a third variable by declaring

a new variable and calling it something that has

multiple words inside of it then it is a habit

of programmers to start with a non capitalized letter

and then the next word is going to be capitalized

so i want to say a variable is called denial

nelson which is my name then i want to start

with non capitalized d and then a capitalized

nelson we can write two words

inside a variable name so we can do this

in order to create a variable name cause this is not going

to work inside the browser now when it comes to variables

we have different types of variables we have something called a var

variable and we also have something called let

and a const variable

now because we still in the beginning of the course i'm not gonna discusse

let and constant to later in this course

because we use this variables for different reasons that

we haven't talked about yet as of not to confuse you

i don't want to talk about let and const until later in this

course so right now you guys can see we did actually declare a variable

called a and what we can do we can actually assign

it something so we actually put some kind of data

inside variable and the way we that

is by going to next line and because we already created

the variable or declaredit

we don't need to do that again so we want to refer this variable a

i just need to write the name of the

variable which is a and set it equal to

some kind data i'm gonna say equal to ten

we can also said equal to a piece of

text or a function or something that we have

inside java script but right now we just gonna go and use numbers

now we have a variable called a i can

go and create a variable called b now the first example

we did actually create the variable first and then we gave it a value

the other way we can do it is we can also go and create

variable first by calling it b and

then directly giving it some kind of data

so we can actually say b is equal

to twenty this actually would be shorter

but in some cases this might not be what we want

to do depending on that application we create using java script

but for now in this example over here we can go ahead

and just create a variable called b and set it equal to twenty

we can actually do the same thing here but just simply

setting a equal to ten now

what i want to do is want take these two variables

and add them together and insert it inside the console

inside the browser and the way we can do that

is by creating a third variable

i'm gonna call this one sum or something

set it equal to a plus

b semicolon

and then i'm gonna go and grab the variable sum

and insert it inside the console log here

then i'm gonna save it and actually you can see we get thirty

inside the browser

and we probably change the number and see the difference

the last piece of data inside the console

so now we can see we get forty when i changed a

to twenty this is how we create variable using

java script and this actually a couple different ways we can do same thing

so want you to go down and next line here

we go ahead and declare a variable called a

comma b

comma sum

semicolon and then down below we can actually add the

values to these variables so i 'm gonna say

a equals to twenty

b is equals to twenty

and sum is equal to a

plus b

and this would be the same things we doing up here

the main difference between these two is that i just went to head and declared

all the different variable names inside one line and

afterwards stored value inside inside the variable names

now a third way we can do this is by going down next line

and say we have variably called a

that is equal to twenty comma

b that is equal to twenty

comma and then we have sum that is

equal to a plus b

semicolon all of these does the exact

same thing it is just a different way that we can write all the different

variable types now just want to point out that why i'm going to make

variables at the beginning of this course here is going to be used

in the first method which is the one up here since it is a bit

easier to over look to a new java script now

another thing i want to show you is we just don't use numbers

inside variables when can also use text or functions

or other kind of data we have inside java script so

if i want to take variables a

which is equal to twenty and changed to

what we call a string which is a string of text

i'm gonna say double quotes and then put some kind of

text in between of the doubles quotes which is how we

create a text string in java script

so i'm going to say my name is

denial save it and then you can see

we get my name is Daniel inside the console

it is very important to point out that you don't write a text string

by not including a double quotes

as if you see i save it would you actually get

uncaught syntax error inside the browser because

it doesn't know what kind of data we trying

to put inside the console now I if i

want to take you all the way back to the beginning in this lesson here

if i have a variable called a that doesn't have any kind of

data assigned to it afterwards actually i'll put it

inside the console

you can see that we get undefined and that's because right

now even though we have declared variable called

a we didn't assign any kind of value to a

yet which is we call undefined which means that

right now there is no data inside variable a

and the reason i want to point this out because if

go ahead and say we have not variable a

but instead we have a is

equal to ten

and then save it you can see we get ten

inside the console inside the browser but wait a minute

we didn't declare a variable a

which is very important to do each time you create a variable using

java script so what is going on here

now if i want to write variable without actually declaring it

first then running it inside the browser then

it is going to declare a variable automatically when we run the script

and this is a bad thing because it allow for

error inside our script and later on

we are gonna talk about variables call lit and const and how we fix this

issue where the code automatically declares

variables inside java script

so this is what i want to talk about when it comes to variables inside java script

and just remember we use variables all the time when we create

scripts using java script so this is very important to remember how

to create variable and how we using them inside our code

so in the future we will get more into variables

how we use them to create scripts using java script

so i hope you guys enjoyed and see you next time