CIS525 - Lecture#7 - September 25, 2000
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CIS 525 9/27/00
More on JavaScript:
Objects in Javascript - created can be similar to objects in C++, with some differences
this.firstname = firstname; => accessing and assigning
An Object Example:
<html><head>
<title> An Object Example </title>
<script language "JavaScript">
function person(firstname, lastname, age) {
this.firstname = firstname;
this.lastname = lastname;
this.age = age;
}
person1 = new person("logan", "blankenschplatz", "87");
Another way of creating/assigning objects:
var test = new Object();
test.field1 = "value1";
Caution: there is no 'spellchecking' in JavaScript!!
Any misspelling may result in an unwanted new field
In JavaScript 1.2, you can assign values thusly:
Object2 = (x:3, y:4, z:5)
This is equivalent to:
var Object2 = new Object();
Object2.x = 3;
Object2.y = 4;
Object2.z = 5;
In JavaScript, "function" is a reserved word:
function square(x) {
return(x*x);
}
Recursion:
function factorial(n) {
if(n<=1)
return(1);
else
return(n*factorial(n-1));
}
For dynamic html:
function printheading(message) {
document.writeln("<H1>" + message + "</H1>");
}
SEE SOURCE CODE IN CHAPTER 19 OF HALL "ShowInfo.html", (best viewed in NotePad), to see the JavaScript code for ShowInfo functionality
In JavaScript, the attribute of an object can be a function return
An example:
this.printStats = printStats;
function printStats() {
document.write(this.firstname + " ");
document.write("age=" + this.age + " ");
}
JavaScript has a parser utility:
parseFloat, (or parseString, parseInt, etc), an example:
parseFloat("137") =>returns 137
parseFloat("137abc") =>returns 137
parseFloat("abc137") =>returns 0, doesn't see a number, and breaks
parseFloat("1abc37") =>returns 1, sees first number, then breaks
Arrays in JavaScript:
myArray = InitArray(10);
myArray[1] = "South Carolina";
myArray[2] = "Oregon"; =>assigning values to indexes
OR:
var squares = nw Array(5);
for(var i = 0; i < squares.length; i++)
squares[i] = i*i;
}
OR:
var squares = new Array(0, 1, 4, 9, 16);
Different methods of assigning values to indexes:
var ArrayObj = new Object();
ArrayObj[0] = "Index zero";
ArrayObj[10] = "Index ten"; =>nothing is placed in indices 1-9
ArrayObj.field1 = "field1"; =>index in this case is actually text, ('field')
ArrayObj["field2"] = "field2"; =>index is text here as well
SEE PAGE 1055 IN HALL FOR CODE "ForIn.html", AN EXAMPLE OF ITERATING OVER ARRAY INDEXES
another example:
for(field in object) =>'field' in this case is the index
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object[field]; =>returns value of 'field' index of object array
Event driven programming:
JavaScript is used for many evnet driven applications
SEE CHAP 19 OF HALL FOR CODE "DontClick.html", (an event program in a form)
Other event functions:
OnChange =>for any change in a specific field/document
OnClick =>for a mouse click
OnBlur =>when focus is removed from an object/input area
OnFocus
OnLoad =>when a page/doc loads
OnMouseOver
OnSelect =>radio buttons or check boxes
OnSubmit =>get/post data, etc
OnUnLoad =>unload page or document
THE LINK BELOW WILL TAKE YOU TO A WEB PAGE ON JAVASCRIPT WITH NUMEROUS EXAMPLES
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Javascript Information (CIS 400 Programming Languages Guide)