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

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- 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

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