Question

This is the script that i am using to fetch a particular cookie lastvisit :

AFTER THE EDIT

// This document writes a cookie
// called from index.php
window.onload = makeLastVisitCookie;

function makeLastVisitCookie() {
var now = new Date();
var last = new Date();
now.setFullYear(2020);
// set the cookie
document.cookie = "lastvisit=" + last.toDateString() + ";path=/;expires=" + now.toGMTString();
var allCookies = document.cookie.split(";");
for( var i=0 ; i < allCookies.length ; i++ ) {
    if(allCookies[i].split("=")[0]== "lastvisit") {
        document.getElementById("last_visit").innerHTML = "You visited this site on" + allCookies[i].split("=")[1];
    } else {
                alert("testing..testing..");
              }
  }
 }

From this script the if part never works though there are 5 cookies stored from my website. (including the cookie that i am saving from this script) What is the mistake that i am making while fetching the cookie named lastvisit ?

Answer 1

You’re splitting the cookie by ; an comparing those tokens with lastvisit. You need to split such a token by = first. allCookies[i] looks like key=val and will never equal lastvisit. Een if allCookies[i] == "lastvisit" is true, the result will still not be as expected since you’re showing the value of allCookies[i + 1] which would be this=the_cookie_after_lastvisit.

if(allCookies[i].split("=") == "lastvisit") { should be:

var pair = allCookies[i].split("=", 2);
if (pair[0].replace(/^ +/, "") == "lastvisit") {

"You visited this site on" + allCookies[i+1]; should be:

"You visited this site on" + pair[1];

The 2 argument of split makes cookies like sum=1+1=2 be read correctly. When splitting cookies by ;, the key may contain a leading space which much be removed before comparing. (/^ +/ is a regular expression where ^ matches the beginning of a string and + one or more spaces.)

Alternatively, compare it directly against a RE for matching the optional spaces as well (* matches zero or more occurences of a space character, $ matches the end of a string):

if (/^ *lastvisit$/.test(pair[0])) {

I’ve tested several ways to get a cookie including using regular expressions and the below was the most correct one with best performance:

function getCookie(name) {
    var cookie = "; " + document.cookie + ";";
    var search = "; " + encodeURIComponent(name) + "=";
    var value_start = cookie.indexOf(search);
    if (value_start == -1) return "";
    value_start += search.length;
    var value_end = cookie.indexOf(';', value_start);
    return decodeURIComponent(cookie.substring(value_start, value_end))
}