javascript

CHAPTER 10 ■ SCRIPTING BOM
function getCookie(name) {
var batch = document.cookie, i, firstCut, secondCut;
i = batch.indexOf(name + "=");
if (i !== -1) {
firstCut = i + name.length + 1;
secondCut = batch.indexOf(";", firstCut);
if (secondCut === -1) secondCut = batch.length;
return decodeURIComponent(batch.substring(firstCut, secondCut));
}
}
Finally, if getCookie() cannot find a cookie named name, let’s convey failure by appending an else
clause that returns false. In just a moment, we will check for false prior to presetting the skin relative to
a visitor’s preference. The final code for getCookie() would be as follows:
function getCookie(name) {
var batch = document.cookie, i, firstCut, secondCut;
i = batch.indexOf(name + "=");
if (i !== -1) {
firstCut = i + name.length + 1;
secondCut = batch.indexOf(";", firstCut);
if (secondCut === -1) secondCut = batch.length;
return decodeURIComponent(batch.substring(firstCut, secondCut));
} else {
return false;
}
}
Setting the User’s Skin Preference
Now for a function to preset the skin to blue, fuchsia, or green depending on the visitor’s preference.
Hmm. Let’s cleverly name it presetSkin(). In its block, declare a local variable named pref, and assign to
it the return value of passing "skin" to getCookie():
function presetSkin() {
var pref = getCookie("skin");
}
So, pref will contain "blue", "fuchsia", or "green" if the visitor set their preference during a
previous visit. Otherwise, pref will contain false. Note that if cookies are disabled, pref will contain
false as well. With this in mind, let’s make sure pref does not contain false before we do anything else.
An if condition and the !== operator will do the job:
function presetSkin() {
var pref = getCookie("skin");
if (pref !== false) {
}
}
Fine and dandy. Now if JavaScript runs the if block, we have a skin to set. Just set the href member
of the skin style sheet to "blue.css", "fuchsia.css", or "green.css" by concatenating pref to ".css":
function presetSkin() {
var pref = getCookie("skin");
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