What is the "best" way to get and set a single cookie value using JavaScript

Question

I want to increment a cookie value every time a page is referenced even if the page is loaded from cache. What is the "best" or most concise way to implement this?

Answer 1

Stolen from http://www.quirksmode.org/js/cookies.html#script

function createCookie(name,value,days) {
    if (days) {
        var date = new Date();
        date.setTime(date.getTime()+(days*24*60*60*1000));
        var expires = "; expires="+date.toUTCString();
    }
    else var expires = "";
    document.cookie = name+"="+value+expires+"; path=/";
}

function readCookie(name) {
    var nameEQ = name + "=";
    var ca = document.cookie.split(';');
    for(var i=0;i < ca.length;i++) {
        var c = ca[i];
        while (c.charAt(0)==' ') c = c.substring(1,c.length);
        if (c.indexOf(nameEQ) == 0) return c.substring(nameEQ.length,c.length);
    }
    return null;
}

function eraseCookie(name) {
    createCookie(name,"",-1);
}

using it:

var oldCount = parseInt(readCookie('hitCount'), 10) || 0;
createCookie('hitCount', oldCount + 1, 7);

as pointed out in the comments, you should cast to an int since cookies are stored and returned as strings. Using foo++ or ++foo will actually cast for you, but it's safer to know exactly what you're working with:

var x = "5";  // x = "5" (string)
x += 1;       // x = "51" (string!)
x += 5;       // x = "515" (string!)
++x;          // x = 516 (number)

Answer 2

Most of the old cookie handling functions I've seen use simple string manipulations for storing an retrieving values, like this example, you can use other libraries, like cookie-js, a small (< 100 lines) utility for cookie access.

I personally use jQuery on my projects, and I use the jQuery Cookie Plugin, it's really simple to use:

var cookieName = "increment";

if ($.cookie(cookieName) == null){
  $.cookie(cookieName, 1, { expires: 10 });
}else{
  var newValue = Number($.cookie(cookieName)) + 1;
  $.cookie(cookieName, newValue, { expires: 10 });
}

Answer 3

the best way is always the simplest:

function getCookie(name) {
  return (name = (document.cookie + ';').match(new RegExp(name + '=.*;'))) && name[0].split(/=|;/)[1];
}

// the default lifetime is 365 days
function setCookie(name, value, days) {
  var e = new Date;
  e.setDate(e.getDate() + (days || 365));
  document.cookie = name + "=" + value + ';expires=' + e.toUTCString() + ';path=/;domain=.' + document.domain;
}

these functions expect the value to be a simple string, but you can always JSON.stringify it if you want or maybe do something else with it...