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:

varfirst = 'Soumya';
letfirst = 'Soumya';
constfirst = '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;