keep checkbox state using cookie in javascript

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Javascript

checkbox

Can you please give me an example code in JavaScript on how to keep the state of a checkbox by creating cookie when I refresh the page?

I have something as the following but I couldn't manage have it run as I expected. I am new in JavaScript.

/*** Simple interface to cookie ***/
Something.Cookie = function (cookieName, defaultValue) {
    function createCookie(name, value, days) {
        var expires = "";
        var date;
        if (days) {
            date = new Date();
            date.setTime(date.getTime() + (days * 24 * 60 * 60 * 1000));
            expires = "; expires=" + date.toGMTString();
        }
        document.cookie = name + "=" + value + expires + "; path=/";
    }
    function readCookie(name) {
        var nameEQ = name + "=";
        var ca = document.cookie.split(';');
        var c;
        for (var i = 0; i < ca.length; i++) {
            c = ca[i];
            while (c.charAt(0) === ' ') {
                c = c.substring(1, c.length);
            }
            if (c.indexOf(nameEQ) === 0) {
                return c.substring(nameEQ.length, c.length);
            }
        }
        return null;
    }
    this.read = function () {
        var val = readCookie(cookieName);
        Something.log("Read " + val + " from cookie " + cookieName);
        return val;
    };
    this.readBoolean = function () {
        return this.read() === "true";
    };
    this.write = function (value) {
        createCookie(cookieName, value, 365);
    };
    this.writeBoolean = function (value) {
        value ? this.write("true") : this.write("false");
    };
    if (this.read() === null) {
        this.write(defaultValue);
    }
    return this;
};

Note:

onclick="GM_setValue("document.myform.mybox.value","true")

could also be a solution instead of using cookies.
However, GM_setValue cannot be called within onclick function.
A solution with GM_setValue would also be helpful because I mainly write this code in Greasemonkey.



Thanks,

Artug