03-variables-and-statements.md

Variables and statements

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;