Including JavaScript in an HTML Page Call an External JavaScript File Including Comments Variables Data Types

JavaScript Basics

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Published by: AT Products LLC.

Including JavaScript in an HTML Page

HTML

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

Call an External JavaScript File

HTML

<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

JavaScript

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