Beware of duplicate cookie values

Came across a strange problem today that I thought I should record since I’ve already wasted enough time investigating it. The problem was that a web site was recording a setting to a cookie each time a page was unloaded; e.g. Preference1. Any page can then read the cookie and take appropriate actions. However, for some reason the preference was not correctly read on any other page. Puzzled I examined the document.cookie property. For some strange reason the value was duplicated; e.g. Preference1=hello; Preference2=bla; Preference1=goodbye. So when the page wrote to the cookie the 2nd version changed but when the cookie was read the 1st version was taken. Once I cleared the cookies for the domain everything went back to normal. The site only has one domain, no sub-domain or anything. Very strange behaviour.

So there it is, an aide memoir for me, but if anyone can provide an explanation I would be grateful. I should mention this was all client side JavaScript.

One thought on “Beware of duplicate cookie values

  1. Walturburk September 19, 2016 / 1:21 pm

    Oh man I just had this issue, took ages to get rid of. I set the path of the cookies to “path=/” and cleared the cookies from my browser and atlast it works.

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