Chapter 4 JavaScript and Dynamic Web pages

Objectives Static Web pages Dynamic Web pages JavaScript Variables Assignments. JavaScript Functions –(prompt(“”,””) –Document.write(“”) –Alert(“”)

Static Web Pages Looks the same and behave in the same manner each time they are loaded into a browser Content doesn’t change It doesn’t specifying dynamic behavior –Example html pages. A programming language is needed….

Dynamic Web pages Properties; –They are the pages that change while you are looking to them, –Varying their contents and responding to your actions.

Variables A variable is name used to symbolize a dynamic value. A variable can be used to represent a value. JavaScript variables: –tempInFahr, X, Y, x, y, Sum, SUM, sum, Sum2Date, Not variables: 2hotforU, salary$, two word,

Assigments = is the assignment statement. The value on the right side assigned to the variable on the left side. x = y+1; myName = john, myname= Jan. Y= 1; Y= 3;

X = X +1 –The current value of X is increased by 1, and the result is assigned back to x. Note; = is assignment operator. == is equality operator.

JavaScript Each Statement in a programming language specifies a particular action that the computer is to carry out, such as changing an image, opening a new window. JavaScript is simple programming language that adding dynamic features to Web pages. How? – the simplest way to add dynamic content to a Web page is to embed Java Script statements directly within the page using tags.

How to insert javascript in a webpage; Use the HTML tag pair and : alert(" your message goes here ");

Greetings hello Word, I like javascrip. …………………….. …………………… ……………………….. ………………….

Greetings firstName = prompt("Please enter your name", ""); document.write(" Hello " + firstName + ", welcome to my Web page. "); Whatever else you want to appear in your Web page...

A function Or Subroutine Take some variables, evaluate this variables and produce an output. –Example; F(x)=x+2, alert(“hello cc312”), prompt(“what is your name”, “”)

Alert(“….”) For creating a pop-up window Alert statement cause a new windows to appear and display a specified message Such as: –alert(" your message goes here ");

Prompt(“Some text”,””) When prompting the user for a value, the programmer can specify ( a string of characters enclosed in quotes) that serve as prompt message, followed by another string that specifies a default value for the prompt. Prompt(“my name is”, “”);

Document.write(“”) Document.write(() statement is used to display a message within the web page. Write statement can display text ( a string) or a combination of text and variables connected with ‘+’. Documet.write(“hello class cc3.12”);

Formating output Any sting in a write statement includes html tags will display just as any other text. –document.write(" Hello "+ firstName + ", welcome to my Web page. “ In general, JavaScript treats any sequence of characters enclosed in quotes as literal text.

Data types Integers –They are numbers, such as 1,2,3,4… Booleans; –True or False values Strings; –They are sequins of any kinds of data types. Such as “Brooklyn college”, “cc312”, this is 4 you”

Number Representation JavaScript automatically displays very large or very small values using scientific notation. –Example would be 1e5, X*10 y =XeY

Programming errors and Debugging Bug refers to an error in a program Debugging is the process of systematically locating and fixing errors in aprogram Three types errors can occur in a program: 1.Syntax errors are simple typographic errors. 2.Run-time errors occur when operations are applied to illegal values, such as dividing by 0. 3.Logic errors represent flaws in the design or implementation of program.

Math library functions Math.sqrt()  returns a square root of the input. Math.max (X,Y)  returns the greater of the two inputs. Math.min(X,Y)  returns the minimum number. Math.floor(2.564)  returns floor of a number, in this example it will return 2. Math.ceil(2.564)  returns ceil of a number, in here it would return 3.