Variables and Constants

Variables

Keyword: let, var

Starts with _ $ letter

Can't be started with number

a
account
account_100
accountNumber (Camelcase)
_accountNumber (Private Variable)

let keyword(Scope Local Variable)

var keyword(Global Variable)

Constants

Keyword: const

Constants can't be changed 

Error :
const price = 40;
price = 50;

if you are unsure about when to set variable or constant, then constant first and later change it to variable. a variable that will not be changed should be constant.

avoid var keyword