Start with letter or an underscore character and

• Start with letter or an underscore character and dollar sign
• Can contain letters, numbers, underscore and dollar sign.
• Variable names are case-sensitive
• Use either underscore or Camel Casing to name a variable with more then one word
• let first_name or let firstName
• Use meaningful names (gagleegoo !!!!! Is not meaningful)
Primitive data types
• There are 6 primitive data types in JavaScript
•
Boolean — true or false
•
Null — no value
•
Undefined — a declared variable but hasn’t been given a value
•
Number — integers, floats, etc
•
String — an array of characters i.e words
•
Symbol — a unique value that's not equal to any other value
• Object
JavaScript Comments
• Single line comment //
• Multiple line comments /* … */
Window and Document Objects
• window.alert(123) or alert(123)
• let num = prompt(‘enter a number’, 10)
• print() <a href=‘#’ onclick=‘print()’>Print this page</a>
• window.location (
• window.open(‘’);
• Document object
• document.write(value) or document.writeln(value)
Syntax error and logical error
s- is when something is misspelled
logical error – when there something that doesn’t make sense

Chapter 2
How to code JavaScript
- Using a text editor like Notepad++ or TextWrangler, enter and edit XHTML, CSS, and
JavaScript files
How to load JavaScript from an external file
<script type="text/javascript" src="sales_tax.js"></script>
Scr = the file name