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2017/03/08

Working with cookies

This is a quick summary of how to work with cookies.

The code below is from https://www.w3schools.com/js/js_cookies.asp.


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<!DOCTYPE html>
<html>
<head>
<script>

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

function getCookie(cname) {
    var name = cname + "=";
    var decodedCookie = decodeURIComponent(document.cookie);
    var ca = decodedCookie.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, 30);
       }
    }
}

</script>
</head>
<body onload="checkCookie()">
</body>
</html>

Note that Chrome doesn't support local cookies. That is, the above code won't work if it's run from a local storage (it will run fine if it's run from a server). However, Internet Explorer, Firefox, Safari, and Opera don't have such problem. For detail, see the discussion at https://productforums.google.com/forum/#!topic/chrome/iow88FsnNhQ.
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