JavaScript Basics

Including JavaScript in an HTML Page

<script type="text/javascript">
  //JS code goes here 

</script> 

Call an External JavaScript File

<script src="myscript.js"></script>
          

Including Comments

Single line comments - // Comment
Multi-line comments - /* comment here */

Variables

var, const, let
var — The most common variable. Can be reassigned but only accessed within a function. Variables defined with var move to the top when code is executed.
const — Can not be reassigned and not accessible before they appear within the code.
let — Similar to const, however, let variable can be reassigned but not re-declared.

Data Types

Numbers — var age = 23
Variables — var x
Text (strings) — var a = "init"
Operations — var b = 1 + 2 + 3
True or fase statements — var c = true
Constant numbers — const PI = 3.14
Objects — var name = {firstName:"John", lastName:”Doe"}

Objects Example

var person = {
  firstName:"John",
  lastName:"Doe",
  age:20,
  nationality:"American"
};