Javascript Recursion

00:46
Recursion is when a function calls itself. This is often useful in mathematics,
such as fi nding the nth number in the Fibonacci series (1, 2, 3, 5,
8, 13, 21…).
function fi bonacci(n) {
if ( n < 2 ) {
return 1;
} else {
return fi bonacci(n-2) + fi bonacci(n-1);
}
}
fi bonacci(5);
8
fi bonacci(10);
89
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Javascript Objects as Arguments

00:45
You may want to write functions that take many arguments, some of
which are optional.
function drawElement( color, border, width, height,
left, top, zIndex) {
// Make and display an element with these variables
}
drawElement("red", 4, null, null, 100, 10);
Function signatures like this aren’t ideal for a couple of reasons:
■ It’s hard to remember the exact order of arguments.
■ You have to specify null values when you want to use the default
value for arguments in the middle of the signature.
■ Did you notice that I forgot to specify a value for zIndex? It’s hard to
count all those arguments correctly!
Passing multiple values in a single object is often a better solution:
function drawElement(options) {
// Make and display an element with the values in options
}
drawElement({
color: "red",
border: 4,
left: 100,
top: 10
});
Specifying default values is a little bit trickier with this technique. You’ll
need to create an object holding all the defaults and merge it with the
options object.
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Javascript search

00:43
search(regexp)
The search() method is the same as indexOf() except that it takes a
regular expression pattern instead of a substring. It also returns -1 if the
pattern isn’t found.
"hello world".search(/[aeiou]/); // Find the fi rst vowel
1
"hello world".search(/\d/); // Find the fi rst digit
-1
match(regexp)
The match() method returns an array containing all the substrings
matching the regular expression and its subpatterns. Unlike the other
search-and-replace methods, it returns null if the pattern doesn’t match.
Here are some simple examples, but I’ll cover this function more in
Chapter 8:
// Find all the vowels
"hello world".match(/[aeiou]/g);
["e", "o", "o"]
// Find "world" regardless of capitalization
"hElLo WoRlD".match(/world/i);
["WoRlD"]
replace(pattern, replacement)
The replace() method works like match() except that it returns a string
with all instances of pattern replaced by the string replacement.
// Remove all non-numeric characters from a phone number
"(310) 555-9876".replace(/\D/g, "");
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JavaScript Popups

00:49
<head>
<script type="text/javascript">

function testPopup() {
window.open( "http://www.google.com/" )
}

</script>
</head>
<body>
<form>
<input type="button" onClick="testPopup()" value="Click">
</form>
</body>


OpenNewWindow =window.open('contact.html','help','toolbar=no,
location=0,directories=no,status=yes,menubar
=0,scrollbars=yes,resizable=yes,
width=300,height=350')





JavaScript Window.Open Arguments


When you open a window, you can set its URL, name, size, buttons, and other attributes, such as whether or not the window can be resized. The basic syntax of this method is


window.open(url, name, features, replace)


where

url is a URL that indicates the document to load into the window.

name is the name for the window (which is useful for referencing later on using the target attribute of HTML links).features is a comma-delimited string that lists the features of the window.

replace is an optional Boolean value (true or false) that indicates if the URL specified should replace the window’s contents or not. This would apply to a window that was already created.

An example of this method is

secondwindow = open("http://www.yahoo.com", "yahoo", "height=300,width=200,

 scrollbars=yes");



<a href="http://www.google.com" target="_blank">Go to Google</a>
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Javascript Making a simple MouseOver

04:42
<a href="http://www.cit.cornell.edu"
onMouseOver="document.logo.src='family.gif ' ; "
onMouseOut ="document.logo.src='harry.gif ' ; " >
<img name="logo" src="harry.gif " border=0></a>


The onMouseOver and onMouseOut attributes are “Event Handlers” that tell the browser what
code to execute when the events occur. You can make it so that the mouseover affects another image on
the page by changing the name of the image accordingly in the event handler code.

We can use a MouseOver to animate a still image when the
mouse rolls over it. In your class files folder you have two images, logoscroll.gif and logostill.gif which
can be used to create this effect.
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Javascript String Constructor

03:52
String is the built-in object corresponding to the primitive string data type. It contains a very large number of methods for string manipulation and examination, substring extraction, and even conversion of strings to marked-up HTML, though unfortunately not standards-oriented XHTML.

The String() constructor takes an optional argument that specifies its initial value:

var s = new String();

var headline = new String("Dewey Defeats Truman");


Because you can invoke String methods on primitive strings, programmers rarely create String objects in practice.

The only property of String is length, which indicates the number of characters in the string.

var s = "String fun in JavaScript";

var strlen = s.length;

// strlen is set to 24


The length property is automatically updated when the string changes and cannot be set by the programmer. In fact there is no way to manipulate a string directly. That is, String methods do not operate on their data “in place.” Any method that would change the value of the string, returns a string containing the result. If you want to change the value of the string, you must set the string equal to the result of the operation. For example, converting a string to uppercase with the toUpperCase() method would require the following syntax:

var s = "abc";

s = s.toUpperCase();

// s is now "ABC"
Invoking s.toUpperCase() without setting s equal to its result does not change the value of s. The following does not modify s:

var s = "abc";

s.toUpperCase();

// s is still "abc"
Other simple string manipulation methods such as toLowerCase() work in the same way; forgetting this fact is a common mistake made by new JavaScript programmers.
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