This script sets various variables in cookies. Primarily for capturing the UTM parameters that are usually sent to Google Analytics. This enables you to submit them along with any form submissions on your website.

utm.js

// adapted from https://github.com/medius/utm_form
// credit: https://github.com/medius

var UtmCookie;

UtmCookie = (function () {
    function UtmCookie(options) {
        if (options == null) {
            options = {};
        }
        this._cookieNamePrefix = '_uc_';
        this._domain = options.domain;
        this._sessionLength = options.sessionLength || 1;
        this._cookieExpiryDays = options.cookieExpiryDays || 365;
        this._additionalParams = options.additionalParams || [];
        this._utmParams = ['utm_source', 'utm_medium', 'utm_campaign', 'utm_term', 'utm_content'];
        this.writeInitialReferrer();
        this.writeLastReferrer();
        this.writeInitialLandingPageUrl();
        this.setCurrentSession();
        if (this.additionalParamsPresentInUrl()) {
            this.writeAdditionalParams();
        }
        if (this.utmPresentInUrl()) {
            this.writeUtmCookieFromParams();
        }
        return;
    }

    UtmCookie.prototype.createCookie = function (name, value, days, path, domain, secure) {
        var cookieDomain, cookieExpire, cookiePath, cookieSecure, date, expireDate;
        expireDate = null;
        if (days) {
            date = new Date;
            date.setTime(date.getTime() + days * 24 * 60 * 60 * 1000);
            expireDate = date;
        }
        cookieExpire = expireDate != null ? '; expires=' + expireDate.toGMTString() : '';
        cookiePath = path != null ? '; path=' + path : '; path=/';
        cookieDomain = domain != null ? '; domain=' + domain : '';
        cookieSecure = secure != null ? '; secure' : '';

        // decode the value first in case it's already encoded - we don't want to encode it twice 
        document.cookie = this._cookieNamePrefix + name + '=' + decodeURIComponent(encodeURIComponent(value)) + cookieExpire + cookiePath + cookieDomain + cookieSecure;
    };

    UtmCookie.prototype.readCookie = function (name) {
        var c, ca, i, nameEQ;
        nameEQ = this._cookieNamePrefix + name + '=';
        ca = document.cookie.split(';');
        i = 0;
        while (i < ca.length) {
            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);
            }
            i++;
        }
        return null;
    };

    UtmCookie.prototype.eraseCookie = function (name) {
        this.createCookie(name, '', -1, null, this._domain);
    };

    UtmCookie.prototype.getParameterByName = function (name) {
        var regex, regexS, results;
        name = name.replace(/[\[]/, '\\[').replace(/[\]]/, '\\]');
        regexS = '[\\?&]' + name + '=([^&#]*)';
        regex = new RegExp(regexS);
        results = regex.exec(window.location.search);
        if (results) {
            return decodeURIComponent(results[1].replace(/\+/g, ' '));
        } else {
            return '';
        }
    };

    UtmCookie.prototype.additionalParamsPresentInUrl = function () {
        var j, len, param, ref;
        ref = this._additionalParams;
        for (j = 0, len = ref.length; j < len; j++) {
            param = ref[j];
            if (this.getParameterByName(param)) {
                return true;
            }
        }
        return false;
    };

    UtmCookie.prototype.utmPresentInUrl = function () {
        var j, len, param, ref;
        ref = this._utmParams;
        for (j = 0, len = ref.length; j < len; j++) {
            param = ref[j];
            if (this.getParameterByName(param)) {
                return true;
            }
        }
        return false;
    };

    UtmCookie.prototype.writeCookie = function (name, value) {
        this.createCookie(name, value, this._cookieExpiryDays, null, this._domain);
    };

    UtmCookie.prototype.writeAdditionalParams = function () {
        var j, len, param, ref, value;
        ref = this._additionalParams;
        for (j = 0, len = ref.length; j < len; j++) {
            param = ref[j];
            value = this.getParameterByName(param);
            this.writeCookie(param, value);
        }
    };

    UtmCookie.prototype.writeUtmCookieFromParams = function () {
        var j, len, param, ref, value;
        ref = this._utmParams;
        for (j = 0, len = ref.length; j < len; j++) {
            param = ref[j];
            value = this.getParameterByName(param);
            this.writeCookie(param, value);
        }
    };

    UtmCookie.prototype.writeCookieOnce = function (name, value) {
        var existingValue;
        existingValue = this.readCookie(name);
        if (!existingValue) {
            this.writeCookie(name, value);
        }
    };

    UtmCookie.prototype._sameDomainReferrer = function (referrer) {
        var hostname;
        hostname = document.location.hostname;
        return referrer.indexOf(this._domain) > -1 || referrer.indexOf(hostname) > -1;
    };

    UtmCookie.prototype._isInvalidReferrer = function (referrer) {
        return referrer === '' || referrer === void 0;
    };

    UtmCookie.prototype.writeInitialReferrer = function () {
        var value;
        value = document.referrer;
        if (this._isInvalidReferrer(value)) {
            value = 'direct';
        }
        this.writeCookieOnce('referrer', value);
    };

    UtmCookie.prototype.writeLastReferrer = function () {
        var value;
        value = document.referrer;
        if (!this._sameDomainReferrer(value)) {
            if (this._isInvalidReferrer(value)) {
                value = 'direct';
            }
            this.writeCookie('last_referrer', value);
        }
    };

    UtmCookie.prototype.writeInitialLandingPageUrl = function () {
        var value;
        value = this.cleanUrl();
        if (value) {
            this.writeCookieOnce('initial_landing_page', value);
        }
    };

    UtmCookie.prototype.initialReferrer = function () {
        return this.readCookie('referrer');
    };

    UtmCookie.prototype.lastReferrer = function () {
        return this.readCookie('last_referrer');
    };

    UtmCookie.prototype.initialLandingPageUrl = function () {
        return this.readCookie('initial_landing_page');
    };

    UtmCookie.prototype.incrementVisitCount = function () {
        var cookieName, existingValue, newValue;
        cookieName = 'visits';
        existingValue = parseInt(this.readCookie(cookieName), 10);
        newValue = 1;
        if (isNaN(existingValue)) {
            newValue = 1;
        } else {
            newValue = existingValue + 1;
        }
        this.writeCookie(cookieName, newValue);
    };

    UtmCookie.prototype.visits = function () {
        return this.readCookie('visits');
    };

    UtmCookie.prototype.setCurrentSession = function () {
        var cookieName, existingValue;
        cookieName = 'current_session';
        existingValue = this.readCookie(cookieName);
        if (!existingValue) {
            this.createCookie(cookieName, 'true', this._sessionLength / 24, null, this._domain);
            this.incrementVisitCount();
        }
    };

    UtmCookie.prototype.cleanUrl = function () {
        var cleanSearch;
        cleanSearch = window.location.search.replace(/utm_[^&]+&?/g, '').replace(/&$/, '').replace(/^\?$/, '');
        return window.location.origin + window.location.pathname + cleanSearch + window.location.hash;
    };

    return UtmCookie;

})();

var UtmForm, _uf;

UtmForm = (function () {
    function UtmForm(options) {
        if (options == null) {
            options = {};
        }
        this._utmParamsMap = {};
        this._utmParamsMap.utm_source = options.utm_source_field || 'USOURCE';
        this._utmParamsMap.utm_medium = options.utm_medium_field || 'UMEDIUM';
        this._utmParamsMap.utm_campaign = options.utm_campaign_field || 'UCAMPAIGN';
        this._utmParamsMap.utm_content = options.utm_content_field || 'UCONTENT';
        this._utmParamsMap.utm_term = options.utm_term_field || 'UTERM';
        this._additionalParamsMap = options.additional_params_map || {};
        this._initialReferrerField = options.initial_referrer_field || 'IREFERRER';
        this._lastReferrerField = options.last_referrer_field || 'LREFERRER';
        this._initialLandingPageField = options.initial_landing_page_field || 'ILANDPAGE';
        this._visitsField = options.visits_field || 'VISITS';
        this._addToForm = options.add_to_form || 'all';
        this._formQuerySelector = options.form_query_selector || 'form';
        this.utmCookie = new UtmCookie({
            domain: options.domain || (location.hostname.indexOf('www.') && location.hostname || location.hostname.replace('www.', '')),
            sessionLength: options.sessionLength,
            cookieExpiryDays: options.cookieExpiryDays,
            additionalParams: Object.getOwnPropertyNames(this._additionalParamsMap)
        });
    }

    UtmForm.prototype.addFormElem = function (form, fieldName, fieldValue) {
        this.insertAfter(this.getFieldEl(fieldName, fieldValue), form.lastChild);
    };

    UtmForm.prototype.getFieldEl = function (fieldName, fieldValue) {
        var fieldEl;
        fieldEl = document.createElement('input');
        fieldEl.type = "hidden";
        fieldEl.name = fieldName;
        fieldEl.value = fieldValue;
        return fieldEl;
    };

    UtmForm.prototype.insertAfter = function (newNode, referenceNode) {
        return referenceNode.parentNode.insertBefore(newNode, referenceNode.nextSibling);
    };

    return UtmForm;

})();

_uf = window._uf || {};

window.UtmForm = new UtmForm(_uf);