What is the shortest function for reading a cookie by name in JavaScript?

Question

What is the shortest, accurate, and cross-browser compatible method for reading a cookie in JavaScript?

Very often, while building stand-alone scri

Answer 1

The following function will allow differentiating between empty strings and undefined cookies. Undefined cookies will correctly return undefined and not an empty string unlike some of the other answers here.

function getCookie(name) {
    return (document.cookie.match('(^|;) *'+name+'=([^;]*)')||[])[1];
}

The above worked fine for me on all browsers I checked, but as mentioned by @vanovm in comments, as per the specification the key/value may be surrounded by whitespace. Hence the following is more standard compliant.

function getCookie(name) {
    return (document.cookie.match('(?:^|;)\\s*'+name.trim()+'\\s*=\\s*([^;]*?)\\s*(?:;|$)')||[])[1];
}