Recently, I delved into learning JavaScript through the guide of Beginning Javascript 5th edition. However, I am stumped by a perplexing JavaScript script
function getCookieValue(name) {
var value = document.cookie;
var cookieStartsAt = value.indexOf(" " + name + "=");
if (cookieStartsAt == -1) {
cookieStartsAt = value.indexOf(name + "=");
}
if (cookieStartsAt == -1) {
value = null;
} else {
cookieStartsAt = value.indexOf("=", cookieStartsAt) + 1;
var cookieEndsAt = value.indexOf(";", cookieStartsAt);
if (cookieEndsAt == -1) {
cookieEndsAt = value.length;
}
value = unescape(value.substring(cookieStartsAt,
cookieEndsAt));
}
return value;}
My query pertains to the inner workings of the indexOf operator in this scenario (despite my prior understanding and use of it). The above snippet is explicated further in the book as follows:
The primary function of this code is to extract the document.cookie string and save it in the 'value' variable
var value = document.cookie;
Subsequently, the aim shifts to locating the desired cookie by using the name passed as a parameter to the function within the 'value' string. This is achieved through the indexOf() method of the String object, demonstrated in the ensuing line:
var cookieStartsAt = value.indexOf(" " + name + "=");
This method will either return the position where the specified cookie is found, or -1 if no such name (and thus, no cookie) exists. The inclusion of " " + name + "=" ensures that unintended matches are avoided. For instance, with cookie names like xFoo, Foo, and yFoo, a search for Foo without a space upfront might erroneously match xFoo first. This distinction is crucial!
What is the logic behind the indexOf() method in this context?? How does it pinpoint the location of the name? Can someone simplify the xFoo, Foo, yFoo example? I'm in need of a more straightforward illustration.