little help understanding this set cookie function?

Question

Rank newbie question (forgive me)--if there's a better forum for this, let me know. I want to set a cookie that expires after thirty days. I've found a response here on stackoverflow and looked at several online explanations on how to set a cookie, but I'm having trouble fully understanding what I'm seeing. Here's the answer given on stackoverflow:

function createCookie(name, value, days) {
    var date, expires;
    if (days) {
        date = new Date();
        date.setTime(date.getTime()+(days*24*60*60*1000));
        expires = "; expires="+date.toGMTString();
    } else {
        expires = "";
    }
    document.cookie = name+"="+value+expires+"; path=/";
}

Here's where you get to correct me when I'm wrong (please):

Line 1 creates a function called createCookie with three arguments, name, value, and days. Those arguments are defined or set when the function is invoked with something like createCookie(testCookie, ?, 30);. I have a question mark in for the argument value because I'm not sure what goes there.

Line 2 establishes two variables, date and expires, without assigning anything to those variables.

Line 3 says if the argument days and then goes right into executing some lines. This is outside my JS understanding, as so far I've done things like if (x > 10) { where x > 10 defines a condition that when true, the code in the following brackets gets executed, and if not, it skips to the else part of the if/else. days isn't a condition as I understand it. I suppose my understanding this part isn't paramount, as long as it works.

Line 4 creates a variable called date and assigns the current date to it.

Line 5 date.setTime(date.getTime()+(days*24*60*60*1000)); does math using the function's argument days to come up with the actual expiration date and assign it to the variable date.

Line 6 expires = "; expires="+date.toGMTString(); assigns a value to the variable expires, but I don't quite follow, as it appears that value is a concatenation of expires which is undefined at that point, plus the value of the argument date expressed as a string? Also, it looks like toGMTString() is deprecated now? Again, it's probably the case that my understanding of this isn't of utmost importance; my lack thereof, though, adds to my overall confusion.

Line 8 sets the cookie with name plus the string "=" plus value plus expires plus the string "; path=/". I still don't know what value should be...

Anyone want to help me understand this, please? Thanks!

The value is "What you want to store in the cookie" and you need to learn about truthy values. — epascarello, Jun 01 '15 at 19:19
For `Line 3`, everything in JavaScript can be used as a condition because every value has either a "truthy" or "falsey" evaluation. The "falsey" values are `0`, `NaN`, `""`, `null`, `undefined` and `false`. — , Jun 01 '15 at 19:22

epascarello · Accepted Answer · 2015-06-01T19:55:32.560

0

Line 1 - value is the data you want to store in the cookie.

createCookie("testCookie", "The value I want to store", 30);

Line 3 - That is a truthy check, it is checking to make sure days is not undefined.

Line 6 - I think you are confusing the string "expires" for the variable expires. And for the GMT, probably written before it was deprecated.

edited Jun 01 '15 at 19:55

answered Jun 01 '15 at 19:24

epascarello

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score 0 · Answer 2 · answered Jun 01 '15 at 19:25

function createCookie(name, value, days) { // this passes in the values for the cookie you want to store
    var date, expires; // set the variables
    if (days) { // check to make sure days is not undefined
        date = new Date(); // sets todays date
        date.setTime(date.getTime()+(days*24*60*60*1000)); // does maths to make it expiry after `day` parameter you passed into the function.
        expires = "; expires="+date.toGMTString(); // sets the expiry date
    } else {
        expires = ""; // else if days is undefined sets nothing to expiry
    }
    document.cookie = name+"="+value+expires+"; path=/"; // sets the cookie.
}

little help understanding this set cookie function?

2 Answers2