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. It 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 false 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"
}