javascript

CHAPTER 10 ■ SCRIPTING BOM
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}
if (i !== -1) {
}
Now that we are sure there is a cookie named with the string in the name parameter, we want to clip
its value from the ticker tape. That cut will begin at the index equivalent to i, plus the character length of
the string in name, plus 1 for the = sign. Remember from Chapter 2 that String.length contains the
number of characters comprising a string. So, for a cookie named skin, that would be 4. Let’s assign the
value of the expression indicating the offset where the value of our cookie begins to firstCut:
function getCookie(name) {
var batch = document.cookie, i, firstCut, secondCut;
i = batch.indexOf(name + "=");
if (i !== -1) {
firstCut = i + name.length + 1;
}
}
As you might imagine, secondCut will be the offset in the document.cookie ticker tape where the
value of our cookie ends. That will either be the first semicolon after firstCut or the end of the string of
cookies. So to find the semicolon, we would again call indexOf() on batch. But this time, we would pass
firstCut as the optional second parameter, which tells JavaScript where to begin its search. Note that i
would work here, too. However, passing secondCut results in a quicker match since it’s closer to the
semicolon than i:
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);
}
}
In the event that our cookie is the last one in batch, secondCut will contain -1. If that’s the case, we
want to overwrite -1 with the length of the string of cookies. That is to say, we want to overwrite it with
batch.length:
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;
}
}
Now for the moment of truth. Clip the value of our cookie from batch by passing
String.substring() the offsets in firstCut and secondCut. However, to decode any whitespace,
commas, or semicolons in the cookie value, be sure to pass the return value of substring() to
decodeURIComponent(). Note that cookie values may not contain any whitespace, commas, or
semicolons, so it’s always best to clean them out just in case. I’ll remind you of that in a bit when we
write the value of our cookie.
Anyway, getCookie() has done its job at this point, so let’s return the cookie value like so: