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HTML Introductory Course

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JavaScript

Purpose

  • JavaScript is used to define the behaviour of webpages.
  • It makes your site interactive.
  • You send and receive information without refreshing the page.

###jQuery

 <link rel="stylesheet" href="https://code.jquery.com/ui/1.12.0/themes/base/jquery-ui.css">
<script src="https://code.jquery.com/jquery-1.12.4.js"></script>
<script src="https://code.jquery.com/ui/1.12.0/jquery-ui.js"></script>

Embedding it

<script>//stuff</script><!-- or --><scriptsrc="script.js"></script>

Syntax and Style Guide

REFERENCELiterals:10000.1Strings:"John Citizen"'a' Strings are just pieces of text Variables:x = 5name = "Kate" Variables store values to be accessed later Operators and Expressions:+ - * /5 * 2 = 10"Dog" + " " + "Cat" Expressions manipulate values Comments: Comments exist after // or between /* and */ Comments aren't run by your browser

Statements, operators, arithmetic and variables example

Write a program that asks for a user's age, and tell them how old they were in a given year

varage=parseInt(prompt("What is your age?"))vardate=newDate().getFullYear();vardifference=parseInt(prompt("What year do you want to know how old you were on this date?"))alert(difference-date+age)

Booleans

In programming, we like to check whether things are true or false

1==1true1!="1"true"hello"=='hello'true1==2false

Arrays

We also often have to store multiple variables in succession

varnames=["Jack","Jill","Mary","Sue"]

Which we can access later

names[0]"Jack"names[3]"Sue"names.length4names[names.length]

Control Statements

We often only want to perform actions if certain conditions are met

If

varpassword=prompt("Password:")if(password=="qwertyuiop"){alert("Welcome")}elseif(password=="poiuytrewq"){alert("You are denied access")}else{alert("Incorrect Password")}

While

varguessedPassword=falsewhile(!guessedPassword){varguess=prompt("Password:")guessedPassword=(guess=="franklin")}alert("Welcome")

For

We can use for loops to iterate over arrays

varnames=["Jack","Jill","Mary","Sue"]varages=[22,31,43,65]for(vari=0;i<names.length;i++){alert(names[i]+": "+ages[i].toString())}

Functions

Functions define code that we want to use more than once

functionguessedPassword(){varguessedPassword=falsewhile(!guessedPassword){varguess=prompt("Password:")guessedPassword=(guess=="franklin")}alert("Welcome")}guessedPassword()

Events

When certain things happen in HTML, we can call JavaScript functions DEMO