Minimal A/B testing

abtest.js

/*
 * Minimal A/B Testing
 *
 * @author Franklin Javier (@franklinjavier)
 * @date Nov 2014
 *
 * @example ABTest('variant1, variant2'); // return one of these
 *
 */

/**
 * @type {string} variants  Variants separated by commas
 *                          Ex - ABTest('test1, teste2, test3, test4');
 * @public
 */
function ABTest( variants ) {

    /**
     * O nome do cookie que sera utilizado
     * @type {string}
     * @private
     */
    var cookieName = '_cookieName';


    /**
     * As variantes passadas por parametro
     * @type {string}
     * @private
     */
    var alternatives = variants.split(',');


    /**
     * Checa se o seed esta gravado no cookie, se nao, 
     * gera um seed novo e grava no cookie
     * @return {number} O seed.
     * @private
     */
    function makeSeed() {

        var seed = readCookie( cookieName );

        if ( ! seed ) {
            seed = Math.floor( Math.random() * alternatives.length );
            setCookie( cookieName, alternatives[ seed ], 30 );
        }

        return seed;
    }


    /**
     * Grava um cookie
     * @param {string} name Nome do cookie
     * @param {number|string} value Valor do cookie
     * @param {number} days Momento que o cookie ira expirar (em dias).
     * @private
     */
    function setCookie( name, value, days ) {

        var expires = '';

        if ( days ) {
            var date = new Date();
            date.setTime( date.getTime()+(days*24*60*60*1000) );
            expires = '; expires=' + date.toGMTString();
        }

        document.cookie = name + ' = ' + value+expires + '; path=/';
    }


    /**
     * Le um cookie
     * @param {string} name Nome do cookie
     * @param {number|string} value Valor do cookie
     * @private
     */
    function readCookie( name ) {

        var match;

        return ( match = new RegExp('(?:^|; )'+ name +'=([^;]+)').exec( document.cookie )) 
            ? window.unescape( match[ 1 ] ) 
            : null;
    }


    /**
     * Remove cookie
     * @private
     */
    function removeCookie() {  
        document.cookie = cookieName + '=; expires=Thu, 01 Jan 1970 00:00:01 GMT;';
    }


    return makeSeed();
    
}