Html JavaScript and CSS

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  • To insert a JavaScript into an HTML page, we use the <script> tag (also use the type attribute to define the scripting language).
    So, the <script type="text/javascript"> and </script> tells where the JavaScript starts and ends:
    By entering the document.write command between the <script type="text/javascript"> and </script> tags,
    the browser will recognize it as a JavaScript command and execute the code line. In this case the browser will write Hello World! to the page:

Transcript

  • 1. HTML/JavaScript/CSS
  • 2. History  What is the relationship between:  SGML  HTML  XHTML  CSS  JavaScript
  • 3. History  Markup  Annotations instructing how the document should appear in print  Word processors use different markup schemes  SGML IBM - Standard Generalized Markup Language Markup instructions stored with ASCII file  Any computer could render document  Lilly Example
  • 4. History  HTML  Tim Berners-Lee created HTML – subset of SGML  Not platform or application specific  Only server software needed to publish file s on the net  Structure versus content  Browser parses HTML file into a tree
  • 5. History  Sample HTML File  <FONT SIZE=14 FACE=Swing>  <B>Bryan Moore</B><BR>  </FONT>  <FONT SIZE=12 FACE=Textile>  1234 Sunset Ave. <BR>  Walla Walla, WA 12345 <BR>  (123)123.4567<BR>  </FONT> Web Applications and Real World Design - Knuckles
  • 6. History Browser parse tree Web Applications and Real World Design - Knuckles
  • 7. History  Problems with extracting data  Need to write a computer program to extract the names and addresses by selecting text strings following font tags  Content and structure of document become intertwined  Not the intention of SGML and original HTML  Cascading Style Sheets  Attempt to separate content and style
  • 8. History  CSS  Can alter the look of entire file with a simple coding change  Can keep styles in an external file  Increases the knowledge needed to code pages Initial rationale of HTML was to appeal to the masses
  • 9. History Parse tree using CSS Still need to reference Information based on “second string after BR” Information is not meaningful Web Applications and Real World Design - Knuckles
  • 10. History  Extensible Markup Language XML  Extensible- can create own tags  Complete separation of content and style Web Applications and Real World Design - Knuckles
  • 11. History  Releases  HTML 4.0 1997  XML 1.0 1998  XML and HTML need to better cooperate  XHTML 1.0 2000  XHTML  Contains elements and attributes of HTML  Elements must have closing tags  Lowercase  Attributes must have values  Attributes in single or double quotes  http://www.w3schools.com/xhtml/default.asp
  • 12. HTML Forms and JavaScript  Client Server Model  Client Side Processing  JavaScript downloaded from web page and processed by the client – typically form checking  JavaScript can interact directly with form data  Server Side processing  Information from a form sent to server for processing  PHP Perl C++  Server can interact directly with the form data
  • 13. HTML Forms and JavaScript  JavaScript  HTML files are text files  JavaScript is interpreted not compiled  Object oriented HTML forms are objects and can be manipulated via JavaScript Dynamic HTML – merger of JavaScript and HTML  Different implementations of DHTML by software companies
  • 14. What is JavaScript  Scripting language (object-oriented)  Lightweight programming language developed by Netscape  Interpreted, not compiled  Designed to be embedded in browsers        Ideal for adding interactivity to HTML pages Detect browser versions Work with info from user via HTML forms Create cookies Validate form data Read and write HTML elements Supported by all major browsers  Internet Explorer has JScript (started in IE3)  http://www.faqts.com/knowledge_base/view.phtml/aid/1380  It’s free, no license required
  • 15. What is JavaScript  Syntax is similar to Java, but it’s not Java per se  Usually JavaScript code is embedded within HTML code using the script tag:  Can have more than one pair of script tags in a page  Semicolons: C++ and JAVA require them but in JavaScript it’s optional
  • 16. What is JavaScript  HelloWorld example program…  <html>          <head><title>JavaScript HelloWorld! </title></head> <body> <script language="JavaScript"> document.write('Javascript says "Hello World!"') </script> </body> </html>  Let’s open it in the browser
  • 17. What is JavaScript  Javascript can be located in the head, body or external file  Head section Ensures script is loaded before trigger event  Body section Script executes when body loads  External Allows scripts to run on several pages  Examples: http://www.w3schools.com/js/js_whereto.asp
  • 18. What is JavaScript  JavaScript statements in head write to the beginning of the body section but don’t violate HTML code already there.  JavaScript statements in body write based on their location  JavaScript interpreted first then HTML interpreted second  Document.write writes to the HTML document not the web page
  • 19. What is JavaScript            <html> <head> <script language=“JavaScript”> document.write (“<b> This is first </b>); </script> </head> <body> Now where does this print on the web page???? <br /> <script language=“JavaScript”> document.write ( “This might be last?”) </script>   </body> </html>  Lets See what the answer is!
  • 20. What is JavaScript  Now, let JavaScript generate HTML for us…  <html>  <head><title>JavaScript HelloWorld!</title></head>  <body>  <script laguage="JavaScript">   document.write("<h2>Javascript-Generated output:</h2> <p>This paragraph generated by JavaScript</p>  <p>It can even insert an image</p>  <img src='../assigns/RayWeb/images/cathedral.jpg' />")   </script>  </body>  </html>  Let’s open it in the browser
  • 21. Identifier Etiquette  Identifier– The name of a variable (or function)  Starts with a letter, can contains digits & underscores  Case Sensitive!!  Should be meaningful to someone reading your code  Good: accountBalance, amountDue  Bad: bal, due,  Just plain wrong: 2bOrNotToBe, +var, total-value
  • 22. Variables  Must declare variables before they’re used in the program  Declare at the top of the program & terminate each statement with ‘;’  Intialize variables when appropriate  Local variables (declared within a function) destroyed after function exit.  Can only be accessed within the function  Example – Note Assignments  var candyBarPrice = 2.50;  var taxRate = .075;  var candyBarsPurchased;
  • 23. Assignment Operator  Assignment ‘looks like’ equal sign but does NOT behave like it  subTotal = subTotal + 1.50  subTotal ‘is assigned the value’ that is currently in subTotal plus the value of 1.50
  • 24. Expressions  An expression is a statement that describes a computation  Usually look like algebra formulas  total = subTotal * taxRate  Operators (+, -, *, /, etc.) have different levels of precedence, similar to algebra  Don’t rely on it! For clarity, use parentheses  w3Schools operator reference page
  • 25. Conditional Statements--if if (some boolean expression is true){ execute the statements within the curly braces, otherwise skip to the first statement after the closing brace } Resume execution here in either case
  • 26. Conditional Statements– if/else if (some boolean expression is true){ execute these statements, otherwise skip to ‘else’ clause } else { execute these statements if boolean expression is false } Resume execution here in either case
  • 27. Conditional Test Program  Diagnostic messages indicate flow of control 1. 2. 3. 4. var variable1 = 1; var variable2 = 2; 1. 2. if(variable1 > variable2){ if(variable1 >= 0){ document.write(“<p> 1 is greater than 0 </p>"); 5. } 6. document.write(“<p>Resuming execution after 'if' 7. statement</p>"); 8. 3. 4. 5. 6. • document.write(“<p>1 is greater than 2</p>"); } else { document.write(“<p>2 is greater than 1</p>"); } document.write("Resuming execution after
  • 28. Strings  Strings are sequences of keyboard characters enclosed in quotes  “Hello World” or ‘Hello World’  Variables can hold strings  var greeting = “Hello World”  String can be empty, i.e., contain no characters  var myAnswer = “”  Use ‘’ (escape symbol) to ‘type’ prohibited characters  b for backspace, n for newline, t for tab, ” for double quote
  • 29. JavaScript Functions – Basic Principles  Abstraction  Experience has taught us that much code is duplicated throughout program  Functions let us write the functionality once, then reuse it
  • 30. JavaScript Functions – Basic Principles  Encapsulation  Functions encapsulate a specific capability or feature  Function name allows us to access a function in our program  Parameterization  We can customize the function’s result by passing in different values each time we use it  Must use functions to write serious software!
  • 31. JavaScript Functions – Basic Principles  Reasons to use functions  Ease of communication  Problem simplification  Easier construction  Code readability  Reusability  Maintainability  In JS, functions are the primary encapsulation mechanism
  • 32. JavaScript Functions – Syntax  JS function syntax function myFunctionName (list of parameters) { ….JS code here… }
  • 33. JavaScript Functions -- Issues  Key issues about using functions  Naming functions  Passing in parameters  Using local variables within functions  How to call (i.e., invoke) functions  How to handle a function’s return value  Where to put JS functions in your webpage
  • 34. JavaScript Functions – Naming  Function names  Name describes what function does  Name is an identifier, so follow JS identifier syntax rules & course coding standards  Example, findMaxValue(‘put some parameters here’)
  • 35. JavaScript Functions -- Parameters  Passing parameters to the function  Parameters provide functions with input  Implicitly declared variables that can be accessed by code within function body  You provide actual input values when you call the function  Parameters are named variables separated by commas  Example, function findMaxValue(num1, num2, num3)
  • 36. JavaScript Functions – Where to put?  Put functions within <script>….</script> tags within the <head> section of the web page <head> <script language=“JavaScript”> declare functions here…. </script> </head>
  • 37. JavaScript Functions – Local Variables  If needed, you can declare local variables within a function  local variable is visible only within the function body after it’s declared  Commonly used to store results of an intermediate calculation
  • 38. JavaScript Functions – Local Variables function findMaxValue(num1, num2,num3) { var tempMax; //local var if (num1 >= num2) { tempMax = num1; } else { tempMax = num2; } if(num3 >= tempMax) { tempMax = num3; } return tempMax; } //end function
  • 39. JavaScript Functions -- Calling  To call a function from your program, add a statement that contains the function name with values for the parameters the function requires  Example…somewhere in the <body>…., var x = 1, y = 4, z = 2; findMaxValue(x, y, z);  What value does the function return?  What happens with the result?
  • 40. JavaScript Functions -- Return  Return keyword tells function to return some value and exit immediately  Function can have multiple return statements but only 1 can be executed in any given function call  Normally used to return the final result of a calculation to the calling program  For an example, see findMaxValue function
  • 41. JavaScript Functions -- Return  Good Example  Uses var maxNumber in calling program  Function’s return value is assigned to maxNumber  Display of maxNumber has correct value for inputs  Code snippet  var x = 1, y = 4, z = 2; var maxNumber = findMaxNumber(x, y, z); document.write(“The maximum is: “ + maxNumber);
  • 42. JavaScript Functions – Parameter Sequence  1. 2. 3. 4. 5. 6. 7. 1. 2. When calling functions, must enter parameters in same order as specified in function argument list. function calculateDensity(height, width, depth, mass){ var volume = height * width * depth; var density = mass / volume; return density; } ………………………………………………. var hth = 2, wth = 3, dth = 4, mass = 10; var result = calculateDensity(2, 10, 3, 4); //returns .07 but correct answer is .42!!!
  • 43. JavaScript Functions – Global Variables  Global variables are those declared outside of functions  Global variables are ‘visible’ from anywhere in the program, including inside functions var globalHello = “Hello!”; function writeHello() { document.write(globalHello); } // outputs “Hello!” Example program
  • 44. JavaScript Functions – Testing  Test each function thoroughly before proceeding with next programming task  Using multiple sets of inputs, be sure to test all possible outcomes  For each test, be sure calling program is properly handling return values
  • 45. JavaScript Functions – Debugging  Use diagnostic output statements to trace program execution  Good places for diagnostic outputs  Just before entering function  Immediately upon entering function  Before/In/After complex logic or computation  Just before function return statement  Immediately after function returns to calling program
  • 46. JavaScript Functions  Built-In Functions  Prompt  Alert  Confirm  http://www.w3schools.com/js/js_popup.asp
  • 47. JavaScript and HTML Forms  JavaScript Objects  Var truck = new Object();  Expression on right is a constructor  Properties truck.color=“white” document.write(color);  Primitives  In JavaScript variable primitive types are number, string and Boolean
  • 48. JavaScript and HTML Forms  Object Model for the Browser Window  Compound object structure is created when a web page loads into a browser Hierarchy  Window is an object, the HTML document is an object and its elements are objects  These objects have primitives associated with them
  • 49. JavaScript and HTML Forms  window [closed, location] history [length] document [bgColor, fgColor, URL, lastmodified,linkColor, vlinkColor]     images [properties] links [properties] frames [properties] forms [properties]
  • 50. JavaScript and HTML Forms  Window object is parent of structure  window.closed is primitive that is Boolean  window.location primitive contains string of the URL of the HTML file  window.document object is primary focus  When web page is loaded the HTML elements assign values to most of these window.document primitives  Often the word window is excluded as in document.write but need it if referring to multiple open windows  Properties can also be objects
  • 51. JavaScript and HTML Forms                   <HTML> <HEAD> <TITLE>Document Properties</TITLE> <SCRIPT LANGUAGE=JavaScript><!-document.write(closed); document.write("<BR>"+ document.bgColor); document.write("<BR>"+document.fgColor); document.write("<BR>"+document.lastModified); //--></SCRIPT> </HEAD> <BODY TEXT="#0000FF" BGCOLOR="#FFFFCC"> <P>Blue text on a yellow background.<BR> <SCRIPT LANGUAGE=JavaScript><!-document.write("<BR>"+ document.bgColor); document.write("<BR>"+document.fgColor); //--></SCRIPT> </BODY> </HTML> Interactive Programming on the Internet Knuckles
  • 52. JavaScript and HTML Forms  false #ffffff #000000 01/10/2001 17:18:30 Blue text on a yellow background. #ffffcc #0000ff Interactive Programming on the Internet, Knuckles
  • 53. JavaScript and HTML Forms  Methods  Behavior associated with an object  Essentially functions that perform an action  Some are built in and others user made  Built-In Methods of the window object  Confirm  Alert  Prompt
  • 54. JavaScript and HTML Forms  User Events  An event occurs when a user makes a change to a form element Ex. Click a button, mouseover an image  Detection of an event done by event handlers  Event handler is an attribute of the HTML button  <form> <input type=button value=“please click” onclick=“function name()”>  </form>
  • 55. JavaScript and HTML Forms <HTML> <HEAD> <SCRIPT LANGUAGE=JavaScript><!-function changecolor(){ document.bgColor="#ff0000"; } //--></SCRIPT> </HEAD> <BODY> <P><FORM > <P><INPUT TYPE=button VALUE="Click Me" onclick="changecolor()">  </FORM>  </BODY>  </HTML>            Interactive Programming on the Internet ,Knuckles
  • 56. JavaScript and HTML Forms  Form Object  Window.document.form  A form is a property of the document but is also an object  Form elements are properties of a form and are also objects  Access to form’s properties is done through the NAME attribute of the FORM tag  Access to the properties of the form elements is done through the NAME attributes of the particular form element
  • 57. JavaScript and HTML Forms Interactive Programming on the Internet ,Knuckles
  • 58. JavaScript and HTML Forms                          <HTML> <HEAD> <SCRIPT LANGUAGE=JavaScript><!-function plus(){ var n1; var n2; n1=document.addmult.num1.value; n2=document.addmult.num2.value; n1=parseFloat(n1); n2=parseFloat(n2); document.addmult.result.value=n1+n2; } function times(){ var n1; var n2; n1=document.addmult.num1.value; n2=document.addmult.num2.value; n1=parseFloat(n1); n2=parseFloat(n2); document.addmult.result.value=n1*n2; } Interactive Programming on the Internet ,Knuckles               //--></SCRIPT> </HEAD> <BODY BGCOLOR="#FFFFCC"> <P><FORM name=addmult> <P>Enter a number in each field: <INPUT TYPE=text NAME=num1 VALUE="" SIZE=5> <INPUT TYPE=text NAME=num2 VALUE="" SIZE=5><BR> <INPUT TYPE=button VALUE="+" onclick="plus()"> <INPUT TYPE=button VALUE="*" onclick="times()"><BR> <INPUT TYPE=reset VALUE="Reset Form"><BR> <TEXTAREA NAME=result ROWS=3 COLS=27 WRAP=virtual></TEXTAREA> </FORM> </BODY> </HTML>
  • 59. JavaScript and HTML Forms Form for submitting info for server side processing Interactive Programming on the Internet ,Knuckles
  • 60. JavaScript and HTML Forms                           <HTML> <HEAD> <SCRIPT LANGUAGE=JavaScript><!-function verify(){ with(document.infoform){ if((fullname.value=="")||(address.value=="")|| (email.value=="")){ alert("You have left one or more fields blank. Please supply the necessary information, and resubmit the form."); } else { display.value="The following information has been added to our guestbook:r"+fullname.value+"r"+ address.value +"r" +email.value; } } } //--></SCRIPT> </HEAD> <BODY BGCOLOR="#FFFFCC"> <P><FORM name=infoform> <P><TABLE BORDER=0> <TR> <TD WIDTH=83> <P>Name: </TD> <TD> <P><INPUT TYPE=text NAME=fullname VALUE="" SIZE=32> </TD> </TR>   <TR>    <TD WIDTH=83> <P>Address: </TD> <TD> <P><INPUT TYPE=text NAME=address VALUE="" SIZE=32> </TD> </TR> <TR> <TD WIDTH=83> <P>E-mail: </TD> <TD> <P><INPUT TYPE=text NAME=email VALUE="" SIZE=32> </TD> </TR> <TR> <TD WIDTH=83> <P><INPUT TYPE=button VALUE="Submit" onclick="verify()"> </TD> <TD> <P><INPUT TYPE=reset VALUE="Clear Your Information"> </TD> </TR> <TR> <TD COLSPAN=2> <P><TEXTAREA NAME=display ROWS=5 COLS=41 WRAP=virtual></TEXTAREA> </TD> </TR> </TABLE>    </FORM> </BODY> </HTML>                         