var=alpahabet or var=numerics?

Question

in javascript i saw that var x=100 which shows output as 100
and in some cases
var x=y
var y=100
document.write(x);
which shows output as 100
what if
var 100=x?

Answer 1

Venkata kalyan chakravarthi sanagapalli

Var is used to declare variables in JavaScript.

There are some rules in every language when naming a variable.

The answer by Rishi Anand clearly states the 5 points to note while naming a variable. Based on that answer let's see few valid and invalid examples.

Valid names:
myVar, _myVar, $myVar, myVar33, my_var

InValid names:
3myVar (shouldnt start with a no.)
my Var (no space),
var (reserved keyword),
my#Var (# not accepted character)
100 ( should nt start with a numberl)

Answer 2

David Carroll it was a mistake on my end 😅, due to wrongly copying the code here.

Y was declared so hoisting would come into play. I have corrected my answer and the example code now.

Answer 3

Venkata kalyan chakravarthi sanagapalli

But for me it's undefined, am I missing something?

var x = y;
var y = 100;
document.write(x) ; // undefined

Anyway, I took above code as an opportunity to go into Hoisting concept in JavaScript for var.
Because of which we get undefined above.

https://code.sololearn.com/Wb2wF7oT3n6n/?ref=app

Answer 4

Morpheus I'm not sure if the question has been updated since your response. It does show that y is declared with var keyword before y is referenced.

As the question is currently worded, hoisting would apply.

Answer 5

var 100=x; will give you syntax error

= is an assignment operator and as per the rule value to the right of = is assigned to the variable to the left of =.
In simple terms L.H.S of = should be a variable and R.HS. of = should be value.

There are few rules to be followed while naming a variable :
i)it can consits of letters,digits,_,and $
ii)it must not begins with digit
iii)it has to be a single world
iv)keywords are not allowed to be used as variables
v)uppercase and lowercase are different

see by yourself whether you variable name is following all the above 5 rules or not

Answer 6

Variable is nothing but a symbolic name given to a memory location.
The property of the variable is that it changes during the execution of program

You are right...var keyword is used to define a variable in JavaScript.
I have already mentioned the rules for naming a variable.

In your case 100 can't be used as variable because it begins with a digit. And as I already mentioned in point ii, variable can't begins with digit

100 is an invalid name for a variable
_100 is a valid name
$100 is a valid name

Answer 7

I don't understand what you said guys I just want to know for what var is used.
And if it is used to define a variable then why a number can't be variable and why alphabets are considered as variable?