What does /;/ and /^ +/ denote?

I recently came across the statement :

var cookies = document.cookie.split(/;/);

and

var pair = allCookies[i].split("=", 2);
if (pair[0].replace(/^ +/, "") == "lastvisit")

In the first statement what does /;/ in the argument of split denote ?

In the second statement what does /^ +/ 开发者_如何学编程in the argument of replace denote ?

These are Regular Expressions.

Javascript supports them natively.

In this particular example:

1. .split(/;/) uses ; as the split character;
2. .replace(/^ +/, "") removes ("") any (+) leading (^) whitespace ().

In both examples, / surround or delimit the regular expression (or "regex"), informing Javascript that you're providing a regex.

Follow the links provided above for more information; regexes are broad in scope and worth learning.

Slashes delimit a regular expression, just like quotes delimit a string.

/;/ matches a semi-colon. Specifically:

var cookies = document.cookie.split(/;/);

Means we split the document.cookie string into an array, splitting it where there are semicolons. So it would take something like "a;b;c" and turn it into ["a", "b", "c"].

pair[0].replace(/^ +/, "")

Just strips all leading whitespace. It turns

"     lastvisit"

into

"lastvisit"

The caret ^ means "beginning of line", it's followed by space, and the + means to repeat the space one or more times, as many as possible.

The // syntax denotes a regular expression (also known as a 'regex').

Regex is a syntax for searching and replacing strings.

The first example you gave is /;/. This is a very simply regex which just searches the string for semi-colons, and then splits it into an array based on the result. Since this is not using any special regex functionality, it could just as easily have been expressed as a simple string, ie split(";") (as has been done with the equal sign in your other example), without making any difference to the result.

The second example is /^ +/. This is more complex and requires a bit of knowledge of how regex works. In short, what it is doing is searching for leading spaces on a string, and removing them.

To learn more about regex, I recommend this site as a good starting point: http://www.regular-expressions.info/

Hope that helps.

I think that /^ +/ means: one or more no-" " characters