Javascript

• Javascript gives your site functionality
• Object-oriented language
  • uses variables, loops, functions, and data to perform things -

    Duckett pages 43-69

• html is content layer .html
• css is presentation layer .css
• javascript is behavior layer .js

How to Use Objects and Methods

• document.write(‘Good afternoon!’);
• consists of an object, member operator, and method with parameters
• javascript runs where found in the html
  • < script > element causes JS to stop and check if it needs to do anything, it tells the browser to load the JS file

Statements

• a script is a series of instructions that a computer can follow, each step is a statement
• JS is case-sensitive
• a statement is individual instruction and each one should start on a new line and end with a ;
  • statements surrounded by curly braced are code blocks
  • these contain a statement and may be grouped together
• write comments to explain code
• multi line comments are pink, to comment = /* */
• single-line comments are gray, to comment = //
• javascript code is green

-a script will have to store information to do its job, use variables to do so

Variables and how to declare them

• var quantity;
  • var is the keyword and the quantity is the variable name

  • once assigned a variable, you can tell it information or assign value

  • var quantity;
  • quantity= 3;

Data types

• numeric data (no comma and there is decimals)
• string data (letters and other characters closed by single or double quotes)
• boolean data (ewither true or false or on and off)
  • miscelleaneous–> arrays, objects, undefined, and null -escaping is done by using a backwards slash \ before any quote mark appears within a string… It tells the interpreter that the character is part of the string not the end

shorthands for creating variables

1. variables declared then values are assigned in statement

   var price =5;
   var quantity =14;
   var total =price*quantity;
   

2. three variables are declared on the same line, then values are assigned to each

 var price, quantity, total; 
price =5;
quantity= 14;
total =price * quantity;

1. two variables are declared and assigned values on the same line. Then one is declared and assigned a value on the next line

var price =5, quantity =14;
var total = price * quantity;

Changing the value of a variable

• you do not need to use var to assign a new value
  • just use the variable name, the = sign, and the new value

  OLD–> instock= true; NEW –> instock=false;

Important Rules for Naming Variables

1. the name must start with a letter, $, or _, and it cannot start with a number
2. the name can contain these afterwords, but you must not use a - or . in a variable name.
3. you cannot use keywords or reserved words.
4. all variables are case sensitive
5. use a name that describes the kind of info that the variable stores to add js file into html –>

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