I'm having trouble reading a cookie in javascript

Question

When there are multiple cookies on my site my javascript code doesn't work. I do not know how to specify the cookie name in javascript because i'm lacking expirience. The cookie is chancing the background color of the atricle.

Does someone know what i am doing wrong?

this is my code.

<div>
    <article id="bg">
        <h1>Kies een kleur en kijk wat voor cookie er wordt aangemaakt</h1>
        <select id="theme" onchange="setColorCookie()">
            <option value="Select Color">Kies een kleur</option>
            <option value="red">Rood</option>
            <option value="orange">Oranje</option>
            <option value="yellow">Geel</option>
            <option value="green">Groen</option>
            <option value="blue">Blauw</option>
            <option value="purple">Paars</option>
            <option value="pink">Roze</option>
            <option value="brown">Bruin</option>
            <option value="black">Zwart</option>
            <option value="white">Wit</option>
        </select>
    </article>
        <script type="text/javascript">
            window.onload = function ()
            {
                if (document.cookie.length != 0) {
                    var nameValueArray = document.cookie.split("=");
                    document.getElementById("theme").value = nameValueArray[1];
                    document.getElementById("bg").style.backgroundColor = nameValueArray[1];
                }
            }

            function setColorCookie()
            {
                var selectedValue = document.getElementById("theme").value;
                if (selectedValue != "Select Color")
                {
                    document.getElementById("bg").style.backgroundColor = selectedValue;
                    document.cookie = "color=" + selectedValue + ";expires=Fri, 5  2019 01:00:00 UTC;";
                }
            }
        </script>
    </div>

Possible duplicate of [What is the shortest function for reading a cookie by name in JavaScript?](https://stackoverflow.com/questions/5639346/what-is-the-shortest-function-for-reading-a-cookie-by-name-in-javascript) — abiratsis, Mar 03 '19 at 22:06

paulsm4 · Answer 1 · 2019-03-04T00:40:23.790

Look here: MDN: Document.cookie or here: JavaScript Cookies.

Instead of var nameValueArray = document.cookie.split("=");, you should do const myCookies = document.cookie.split(";");. Because:

https://developer.mozilla.org/en-US/docs/Web/API/Document/cookie
allCookies = document.cookie;
In the code above allCookies is a string containing a semicolon-separated list of all cookies (i.e. key=value pairs).

For example:

 allCookies = document.cookie;  // allCookies <= "cookie1=cow; cookie2 = pig; cookie3=  chicken;"
 cookiesArray = allCookies.split(';');  // cookiesArray[] <= ["cookie1=cow", "cookie2 = pig", "cookie3=  chicken"]

One more suggestion:

Modify your code like this:

<script type="text/javascript">
    window.onload = function () {
        const allCookies = document.cookie;
        const cookiesArray = allCookies.split(';');
        alert('allCookies:' + allCookies);
        alert('cookiesArray:' + JSON.stringify(cookiesArray));
        if (document.cookie.length != 0) {
           ...

Re-run your program. When "onload()" triggers, you'll see two successive "alert" pop-ups.

This should help better explain what's going on.
Please - PLEASE - post back if you have questions; if there's something you "don't get". This isn't a difficult concept - I definitely want you to understand it.

I don't buy that disingenuous "total noob" act. You either make the effort to read a couple of paragraphs and try to understand two lines of code ... or you don't. If you have further questions - feel free to ask. Otherwise... PS: I *TOLD* you "what you were doing wrong: `split('=')`. Try `split(';')` instead. Because the "delimiter" separating the "cookies" in the "string" is ";". The delimiter for "key=value" is "=". You're splitting "cookies" on the wrong delimiter! — paulsm4, Mar 03 '19 at 22:30
No problem. Here's what you need to do: 1) Get the entire string (a ";" delimited list of cookies): `document.cookie`. 2) Split them into an array of individual cookies: `.split(';')`, 3) Find the cookie (`key=value`) you're looking for in the array, and finally 4) Split the name and value into an array: `.split('=')`. Q: Make sense now? And thank you for following up with questions. That counts for a lot. Really :) — paulsm4, Mar 04 '19 at 18:32

score 1 · Answer 2 · answered Mar 03 '19 at 22:05

Take a look at w3schools:

function setCookie(cname, cvalue, exdays) {
  var d = new Date();
  d.setTime(d.getTime() + (exdays * 24 * 60 * 60 * 1000));
  var expires = "expires="+d.toUTCString();
  document.cookie = cname + "=" + cvalue + ";" + expires + ";path=/";
}

function getCookie(cname) {
  var name = cname + "=";
  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);
    }
    if (c.indexOf(name) == 0) {
      return c.substring(name.length, c.length);
    }
  }
  return "";
}

function checkCookie() {
  var user = getCookie("username");
  if (user != "") {
    alert("Welcome again " + user);
  } else {
    user = prompt("Please enter your name:", "");
    if (user != "" && user != null) {
      setCookie("username", user, 365);
    }
  }
}

I'm having trouble reading a cookie in javascript

2 Answers2