Semicolons used to end a statement. You can choose to not write them (because there is ASI: Automatic Semicolon Insertion in Javascript).

Declaring a variable:

var**first** = 'Soumya';

let**first** = 'Soumya';

const**first** = 'Soumya';

(here value is 'Soumya')

• let and const were introduced in ES6 (newer).

• var and let can be updated but not const.

  var x = 'hey';
  y = 'hi';
  
  let cool = true;
  cool = false;
  
  const age = 10;
  age = 11; // wrong: throws error
  

• In strict mode, we have to define a variable first before assigning a value to it.

  dog = 'snickers'; // bad coding, don't do this
  console.log(dog); // snickers (no error) 
  
  'use strict';
  dog = 'snickers'; // error: dog is not defined
  

• If we write var dog; dog is undefined.

• Scoping:

  • var : function scoped (only available inside parent functions)

  • let and const : block scoped (available inside a block denoted by { } )

• Opinion (what to use): Use const by default; if the value of the variable needs to change then use let. Almost never use var.

• Variable naming conventions:

  • Should not start with capital unless they are a class.
  • Must start with a-z or _ or $.
  • If a variable is multi-word, you can use:
    • Camel-case: let iLovePizza = true;
    • Upper Camel case (in case of classes): ILovePizza
    • Snake case: let i_love_pizza=true;