How to detect that JavaScript and/or Cookies are disabled?

Assuming JavaScript is enabled, this will tell you if cookies are enabled or not. Works in old browsers.

// returns 1 or 0 instead of true or false. Returns null if inconclusive.
function cookiesEnabled() {
    var i, j, cookies, found;
    if (navigator.cookieEnabled===false) return 0;
    document.cookie = 'testcookiesenabled=1';
    for (i=0; i<2; i++) {
        found = false;
        cookies = document.cookie.split(';');
        j = cookies.length;
        while(j--) {
            while (cookies[j].charAt(0)==' ') {// trim spaces
                cookies[j] = cookies[j].substring(1);
            }
            if (cookies[j].indexOf('testcookiesenabled=')==0) {
                found = true;
                break;
            }
        }
        if (!found) {
            return i;
        }
        // Delete test cookie.
        document.cookie = 'testcookiesenabled=; expires=Thu, 01 Jan 1970 00:00:01 GMT';
    }
    // Results inconclusive.
}

To display a message only when JavaScript is disabled use

<noscript>JavaScript is disabled. Please enabled JavaScript.</noscript>

For checking cookies you can use:

function checkCookie(){
    var cookieEnabled = navigator.cookieEnabled;
    if (!cookieEnabled){ 
        document.cookie = "testcookie";
        cookieEnabled = document.cookie.indexOf("testcookie")!=-1;
    }
    return cookieEnabled || showCookieFail();
}

function showCookieFail(){
  // do something here
}


// within a window load,dom ready or something like that place your:
checkCookie();

And for checking JavaScript use a <noscript> tag with some kind of message inside

Update (6/25/18):

A lot of these posts, including mine, are taking snippets from Modernizr. They will all eventually become outdated as the Modernizr code gets updated.

I think the best answer to this question should be to use Modernizr directly.

if (Modernizr.cookies) {
  // supported
} else {
  // not-supported
}

---

Original Answer (5/11/17):

This is taken straight from Modernizr and works in more browsers than other solutions in this post.

https://github.com/Modernizr/Modernizr/commit/33f00fbbeb12e92bf24711ea386e722cce6f60cc

function checkCookie(){
    // Quick test if browser has cookieEnabled host property
    if (navigator.cookieEnabled) return true;
    // Create cookie
    document.cookie = "cookietest=1";
    var ret = document.cookie.indexOf("cookietest=") != -1;
    // Delete cookie
    document.cookie = "cookietest=1; expires=Thu, 01-Jan-1970 00:00:01 GMT";
    return ret;
}

As the cookie detection didn't work in IE 11, I suggest the Modernizr approach:

function areCookiesEnabled() {
    try {
      document.cookie = 'cookietest=1';
      var cookiesEnabled = document.cookie.indexOf('cookietest=') !== -1;
      document.cookie = 'cookietest=1; expires=Thu, 01-Jan-1970 00:00:01 GMT';
      return cookiesEnabled;
    } catch (e) {
      return false;
    }
}

https://github.com/Modernizr/Modernizr/blob/master/feature-detects/cookies.js