Javascript variables

Hey folks. We shall go through one of the basic units of storage - variables.

Variables are containers that store values.
Javascript is dynamically typed language - run time data types i.e, a variable can be used to store any type of data - be it strings, integers, floating numbers etc.

Naming of variables

Variables are also known as identifiers similar to other programming languages.Variable naming has certain rules to be followed.
- variable name can begin only with a letter or underscore ( _ ).
- variable names can contain letters(a-z/A-Z), numbers(0-9) and dollar sign($).
- variable names can not contain any space or tabs.
- variable names are case-sensitive.
```
  var place1 = "Hassan";
  let _phoneNumber = 9001001121;
  const name$ = "Meghana";
  const NAME$ = "Deepika"; //name$ and NAME$ are different variables - case sensitive
  let country name = "INDIA" //error -can not contain spaces
```

Ways to declare a variable

- var (ES5)
- let and const(ES6)

1. Using `var` keyword

Note: typeof operator returns a string indicating the data type of the variable

var keyword is used to declare variables which can be used globally.

  var coins = 1
  typeof a //returns type of the value variable 'coins' holds 
  "number"

  coins = true
  typeof a
  "boolean"

  coins = []
  typeof a 
  "object"

  coins = null
  typeof a 
  "object"

  var coins = "Javascript" //redeclaration of same variable allowed when var keyword is used
  typeof a 
  "string"

2. Using `let` keyword

let keyword is used to declare variable in local scope of a block statement i.e, these variables can be accessed wherever they are declared only.
```
  let chocolates = 3;
  chocolates = 0;
  let chocolates = 10; //Syntax error for redeclaration thrown unlike var keyword usage
```

3. Using `const` keyword

const keyword is used to declare variable in local scope where it can be accessed but cannot be reinitialised and redeclared

  const chocolates = 3;
  chocolates = 10; //Syntax error for re-initialisation thrown unlike var and let keyword usage

Comparisons between `var`, `let`, `const`

var	let	const
ES5	ES6	ES6
redeclaration of variable allowed	redeclaration not allowed	redeclaration not allowed
re-initialisation allowed	re-initialisation not allowed	re-initialisation not allowed
re-assignment of value to variable allowed	re-assignment of value to variableallowed	re-assignment of value to variable not allowed
functional/global scope	lexical/block scope	lexical/block scope
Hoisted	not hoisted	not hoisted

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Javascript variables

Javascript variables

Naming of variables

Ways to declare a variable

1. Using var keyword

2. Using let keyword

3. Using const keyword

Comparisons between var, let, const

1. Using `var` keyword

2. Using `let` keyword

3. Using `const` keyword

Comparisons between `var`, `let`, `const`