Ifi7174 lesson3

IFI7174.DT – Lesson 3
JavaScript

JavaScript
• Is a lightweight
– Object Oriented Programming (OOP) language
• Why JavaScript?
– It helps you to add behaviors into your webpages
– It changes HTML Content
– It changes HTML Styles (CSS)
2015 @ Sonia Sousa 2

JavaScript
• Is typically used in browsers
– to power dynamic websites.
• add functionality;
• validate input, and
• communicate with web servers
• JS code is loaded and ran
– Inline within HTML code <script> tags
– In blocks
• <script> JS code </script>

JavaScript
• Can be:
– Load as an external scripts
• External
– Inline within HTML code <script> tags
– Embedded
• <head>
– functions
• <body>
– event change
<script src="myScript.js"></script>
<script>document.write("<h1>Hello, there!</h1>"); </script>
<head>
<title>Embedded JS Example</title>
<script>
document.write("Oops");
</script>
</head>

External JS Advantages
• It separates HTML and code
• It makes HTML and JavaScript easier to read
and maintain
• Cached JavaScript files can speed up page
loads

JS Embedded in HTML
<script>
function myFunction()
{
document.write("Oops! The document disappeared!");
}
</script>
<button onclick="myFunction()">Try it</button>
• <head> </head>
• <body> </body>

JS inline with HTML
<h1>My Web Page</h1>
<p id="demo">A Paragraph</p>
<button type="button" onclick="myFunction()">Try it</button>
<script>
function myFunction() {
document.getElementById("demo").innerHTML = "Paragraph
changed.";
}
</script>
• <body> </body>

The Document Object
• When an HTML document is loaded into a web
browser,
– it becomes a document object.
• The document object
– provides properties and methods
• to access all node objects, from within JavaScript
– represents
• the root node of the HTML document
– It controls the
• element, text, attribute, and comment nodes

Document Object Model (DOM)
• starts by…
1. browser window itself
2. document page,
3. the elements included on
the page; and
4. their attributes.
Source: Wikipedia
The object hierarchy

How JS and the DOM cooperate
• When a web page is loaded,
– The browser creates a DOM of the page
• Like a tree
Source: w3schools2015 @ Sonia Sousa 10

DOM
Window
documen
t
meta
Textbox
Radio
button
head body
form[] link Imagestitle div ul
li
Establish the Order of things

How JS and the DOM cooperate
• JavaScript can change
– the HTML elements in the page
– the HTML attributes in the page
– the CSS styles in the page
• JavaScript can react to
– the events in the page
• This is done by
– object notation

Object notation
• Access to elements
– be referenced using dot notation
• starting with the highest-level object
– (i.e., window).
» But as the window is in the top hierarchy do not need to
be refereed
– Objects can be referred to
• by name; or id; or by their position on the page
document.getElementById("demo").innerHTML = "Hello JavaScript”;

JavaScript Syntax
• Basic rules
– Ends with ; (semi-colons)
– ! is case sensitive !
• Comments
– double slash (//)
• 1 line comment
– between /* and */
• More than 1 line comment

JS programs
• A program is a
– list of "instructions” to be "executed" by the
computer
– These instructions are called statements
• JS statements are separated by semicolons ;
• A statement composed of:
– Values, Operators, Expressions, Keywords, and
Comments.

JavaScript statements
• Statements includes
– Values, Operators, Expressions, Keywords, and
Comments
– Values are
• Literal or variables
– Functions are
• a block of code that can execute some action
– Events are
• actions triggered by someone

Values
• Literal values are
– Numbers
• with or without decimals (10.50 or 1001)
– Strings
• Double or single quotes ("John Doe” ‘John Doe’)
– Variables
• Are used to store data (var x; x = 6;)

JS Keywords
• To identify the JavaScript action to be performed.
Keyword Description
break Terminates a switch or a loop
continue Jumps out of a loop and starts at the top
do ... while
Executes a block of statements, and repeats the block, while a condition is
true
for Marks a block of statements to be executed, as long as a condition is true
function Declares a function
if ... else Marks a block of statements to be executed, depending on a condition
return Exits a function
switch Marks a block of statements to be executed, depending on different cases
try ... catch Implements error handling to a block of statements
var Declares a variable

JS Statements
• A statement is the line of code that tell
– the browser to execute something
document.getElementById("demo").innerHTML = "Hello!";
• JavaScript statements
Var x = 5;
var y = 6;
var z = x + y;
document.getElementById("demo").innerHTML = z;

JavaScript Statements
• Giving a command to the browser
<script>
{
document.write("Oops! The document
disappeared!");
}
</script>
<script>
{
document.write("Oops! The document
disappeared!");
}
</script>

JS code and Blocks
JS code blocks
JS functions
<script>
{
}
</script>
<script>
1. document.write("<h1>Hello, there!</h1>");
2. document.getElementById("demo").innerHTML="Hello Dolly";
3. document.getElementById("myDIV").innerHTML="How are you?”;
</script>
• Define statements to be executed together
• JavaScript functions are statements grouped in blocks

JS and HTML Styles (CSS)
• JavaScript can change
– HTML elements
– (CSS) Styles
– Or validate input (data)
• Using methods, conditional and fuctions
• For instance, to change the text
– It uses getElementById() method
document.getElementById("demo").innerHTML = "Hello
JavaScript”;

JavaScript Variables
• variables are "containers" of information
– We can name it using letters (like x)
• The variable can contain
– Letter, numerical values or expressions
var x=5;
var y=6;
var z=x+y;
"declaring" a variable
assign a value
var carname;
carname="Volvo";

Declaring (Creating) JS Variables
• Primitive data types
– Number
var x = 5;
– String
var carname = “Volvo XC60";
– Boolean
var x = true;
var y = false;

Declaring (Creating) JS Variables
• JS Array
var cars=new Array();
cars[0]="Saab";
cars[1]="Volvo";
cars[2]="BMW";
var cars = ["Saab", "Volvo", "BMW"];
• JavaScript Objects
var person = {firstName:"John", lastName:"Doe",
age:50, eyeColor:"blue"};

Object (Properties and Methods)
• data (variables) as objects
– they have properties
– they have methods
Object Properties Methods
Car car.name = Fiat
car.model = 500
car.weight = 850kg
car.color = white
car.start()
car.drive()
car.brake()

JS Operators
• Operators are used to
– assign values to variables using (=)
• var x = 5; var y = 6;
• Arithmetic operators
• Comparison operators
• Logical operators
Operator Description
+ Addition
- Subtraction
* Multiplication
/ Division
% Modulus
++ Increment
-- Decrement

JS Operators
Opera
tors
example results
+ x=y+2 Addition x=7
- x=y-2 Subtraction x=3
* x=y*2 Multiplication x=10
/ x=y/2 Division x=2.5
++ x=++y Increment x=6
-- x=--y Decrement x=4
== x==8 equal to false
!= x!=8 Not equal to true
> x>8 greater than false
< x<8 less than true
>= x>=8 greater than or equal to false
<= x<=8 Less tan or equal to true
&& (x < 10 && y > 1) and true
|| (x==5 || y==5) or false
! !(x==y) not true
Logical
Comparison
Arithmetic

Assignment Operators
Operator Example Same as
Resul
t
= x=y
+= x+=y x=x+y
-= x-=y x=y-2
*= x*=y x=x*y
++ x=++y Increment x=6
-- x=--y Decrement x=4
== x==8
!= x!=8
> x>8
< x<8
>= x>=8
<= x<=8
&& (x < 10 && y > 1)
|| (x==5 || y==5)
! !(x==y)

JS Expressions
• Combine values, variables, and operators
– The computation is called an evaluation
• 5 * 10 evaluates to 50
– can also contain variable values
• x * 10
• "John" + " " + "Doe"

JavaScript Functions
• is a block of code designed to perform a
particular task.
– A JavaScript function is executed when
"something" invokes it (calls it).
function name(parameter1, parameter2,
parameter3) {
code to be executed
}

Function Syntax
function name(parameter1, parameter2, parameter3) {
code to be executed
}
<!DOCTYPE html>
<html>
<head>
<script>
{
alert("Hello World!");
}
</script>
</head>
<body>
<button onclick="myFunction()”> Try it </button>
</body>
</html>
Function name
Code to execute
Call function

Function Invocation
• The code inside the function will execute
when "something” happens
– an event occurs (when a user clicks a button)
– it is invoked (called) from JavaScript code
– Automatically (self-invoked)

JavaScript Functions
• A block of code that will be executed when
"someone" calls it
<script>
{
}
</script>
<script>
{
}
</script>
Code Block
Call
function

Return values
• Functions often compute a return value.
var x = myFunction(4, 3);
// Function is called, return value will end up in
x
function myFunction(a, b) {
return a * b;
// Function returns the product of a and b
}

Function with Arguments
</head> <body>
<button onclick="myFunction('Bob','Builder')">Try it</button>
<script>
function myFunction(name,job)
{
alert("Welcome " + name + ", the " +
job);
}
</script>
<script>
myFunction(argument1,argument2)
{
some code
}
</script>

Using ID with function
</head> <body>
<p id="demo"></p>
<script>
document.getElementById("demo").innerHTML=myFunction(4,3);
</script>
<script>
function myFunction(a,b)
{
return a*b;
}
</script>
<script>
myFunction(argument1,argument2)
{
some code
}
</script>

JavaScript Events
• Is something the browser does, or something a user does
– Event handlers
• used to handle, and verify, user input, user actions, and browser
actions.
– HTML events
• An HTML web page has finished loading
• An HTML input field was changed
• An HTML button was clicked
<some-HTML-element some-event="some JavaScript">
<button onclick="this.innerHTML=Date()">The time is?
</button>

HTML DOM Events
Event Description
onchange An HTML element has been changed
onclick The user clicks an HTML element
onmouseover The user moves the mouse over an HTML element
onmouseout
The user moves the mouse away from an HTML
element
onkeydown The user pushes a keyboard key
onload The browser has finished loading the page
onmouseenter occurs when the pointer is moved onto an element
onmousedown the user presses a mouse button over an element

JavaScript Strings
• String have Properties and Methods
– Primitive value
• var firstName = "John”
var x = "John";
– String objects
• var firstName = new String("John")
var y = new String("John");

JavaScript Strings
Method Description
charAt() Returns the character at the specified index (position)
concat() Joins two or more strings, and returns a copy of the joined strings
indexOf()
Returns the position of the first found occurrence of a specified value in a
string
lastIndexOf()
Returns the position of the last found occurrence of a specified value in a
string
localeCompare() Compares two strings in the current locale
replace() Searches a string for a value and returns a new string with the value
search() Searches a string for a value and returns the position of the match
split() Splits a string into an array of substrings
toLocaleLowerCase() Converts a string to lowercase letters, according to the host's locale
toLocaleUpperCase() Converts a string to uppercase letters, according to the host's locale
toLowerCase() Converts a string to lowercase letters
toString() Returns the value of a String object
toUpperCase() Converts a string to uppercase letters
trim() Removes whitespace from both ends of a string
valueOf() Returns the primitive value of a String object

JavaScript Numbers
• toString() Method
– returns a number as a string
var x = 123;
x.toString();
// returns 123 from variable x
(123).toString();
// returns 123 from literal 123
(100 + 23).toString();
// returns 123 from expression 100 + 23

JavaScript Math Object
• Allows you to perform mathematical tasks.
Math.random(); // returns a random number
Math.min() Math.max()
Math.random()
Math.round()

JavaScript Dates
• lets you work with dates
– Date()
– Date(milliseconds)
– Date(dateString)
– Date(year, month, day, hours, minutes, seconds,
milliseconds)
<script>
var d = new Date();
document.getElementById("demo").innerHTML = d;
</script>

Date and time Methods
Method Description
getDate() Get the day as a number (1-31)
getDay() Get the weekday as a number (0-6)
getFullYear() Get the four digit year (yyyy)
getHours() Get the hour (0-23)
getMilliseconds() Get the milliseconds (0-999)
getMinutes() Get the minutes (0-59)
getMonth() Get the month (0-11)
getSeconds() Get the seconds (0-59)
getTime() Get the time (milliseconds since January 1, 1970)
setDate() Set the day as a number (1-31)
setFullYear() Set the year (optionally month and day)
setHours() Set the hour (0-23)
setMilliseconds() Set the milliseconds (0-999)
setMinutes() Set the minutes (0-59)
setMonth() Set the month (0-11)
setSeconds() Set the seconds (0-59)
setTime() Set the time (milliseconds since January 1, 1970)

JavaScript Output
• Display Possibilities
– window.alert()
– document.write()
– innerHTML
– console.log()

window.alert()
• Is used to display data as a window alert
<script>
window.alert(5 + 6);
</script>

document.write()
• For writing information in the document
– Useful for testing purposes or to replace information
in a HTML page
</script>
document.write("<h2>“your name” </h2>");
document.write("<img src='me.jpg' width='180'>");
</script>
<p>My first paragraph.</p>
<button type="button" onclick="document.write(5 +
6)">Try it</button>

innerHTML
• To access an HTML element by using
– the document.getElementById(id) method.
• id attribute defines the HTML element
• innerHTML property defines the HTML
<p>My First Paragraph</p>
<p id="demo"></p>
<script>
document.getElementById("demo").innerHTML
="<h3>Welcome</h3>";
</script>

JS and HTML
• Finding HTML elements
– by id
– by Tag Name
– by Class Name
• Changing elements in HTML
– Write in html
– HTML Content
– Value of an Attribute
document.getElementById("intro");
getElementsByTagName("p");
document.getElementsByClassName("intro");
document.write( );
document.getElementById("p1").innerHTML="New text!";
document.getElementById("image").src="landscape.jpg";

JS and CSS
• Changing HTML Style
document.getElementById("p2").style.color="blue";
document.getElementById("p2"). background.color="blue";
document.getElementById("demo").innerHTML="<h3>Welcome</h3>";

Js and events
• When an element is clicked on
• Onclick
• onSubmit
– Or reacting to an event
• onmouseover and onmouseout

Window Object Methods
Method Description
alert() Displays an alert box with a message and an OK button
close() Closes the current window
confirm() Displays a dialog box with a message and an OK and a Cancel button
createPopu
p() Creates a pop-up window
moveBy() Moves a window relative to its current position
moveTo() Moves a window to the specified position
open() Opens a new browser window
print() Prints the content of the current window
prompt() Displays a dialog box that prompts the visitor for input
resizeBy() Resizes the window by the specified pixels
resizeTo() Resizes the window to the specified width and height
scroll() Deprecated. This method has been replaced by the scrollTo() method.
scrollBy() Scrolls the document by the specified number of pixels
scrollTo() Scrolls the document to the specified coordinates
stop() Stops the window from loading

Conditionals
• If , if else, else if
– Execute the code if a specified condition is true
if (condition) {
block of code to be executed if the condition is true
} else {
block of code to be executed if the condition is false
}

Logic of an if-else statement
condition
evaluated
statement1
true false
statement2
552015 @ Sonia Sousa

Conditionals
• Switch – Case
– perform different actions based on different
conditions.
switch ( expression )
{
case value1 :
statement-list1;
break;
case value2 :
statement-list2;
Break;
case ...
default:
break;
}
switch
and
case
are
reserved
words
If expression
matches value2,
control jumps
to here

The For Loop
• to run the same code over and over again
– each time with a different value.
for (statement 1; statement 2; statement 3) {
code block to be executed
}
– Statement 1
• is executed before the loop (the code block) starts.
– Statement 2
• defines the condition for running the loop (the code block).
– Statement 3
• is executed each time after the loop (the code block) has been
executed.

Loops
var i;
for (i = 0; i < 10; i++) {
document.getElementById("demo").innerHTML += i +
"<br>";
}
0
1
2
3
4
5
6
7
8
9

Conditionals
• If
if (time<20)
{
x="Good day";
}
else
{
x="Good evening";
}
function timegess()
{
var x="";
var time=new Date().getHours();
if (time<10)
{
x="Good morning";
}
else if (time<20)
{
x="Good day";
}
else
{
x="Good evening";
}
}
</script>

Conditionals
• Switch - Case
– More than 1 condition
• select one of many blocks
of code to be executed
switch(n)
{
case 1:
execute code block 1
break;
case 2:
execute code block 2
break;
default:
code to be executed if n is different from case 1 and
2
}
switch (d)
{
case 0:
x="Today it's Sunday";
break;
case 1:
x="Today it's Monday";
break;
case 2:
x="Today it's Tuesday";
break;
case 3:
x="Today it's Wednesday";
break;
case 4:
x="Today it's Thursday";
break;
case 5:
x="Today it's Friday";
break;
case 6:
x="Today it's Saturday";
break;
}

JavaScript Form Validation
• A form can be validated using JavaScript
function validateForm() {
var x = document.forms["myForm"]["fname"].value;
if (x == null || x == "") {
alert("Name must be filled out");
return false;
}
}
<form name="myForm" action="demo_form.asp" onsubmit="return
validateForm()" method="post">
Name: <input type="text" name="fname">
<input type="submit" value="Submit">
</form>

EXERCISE 3 – JAVASCRIPT

Ifi7174 lesson3

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Ifi7174 lesson3