The following function can be used to get some basic information about the current browser and return it in JSON format.

function getBrowserInfo() {
    var
        json = "[{",
        
        /* The array containing the browser info */
        info = [
            navigator.userAgent, // Get the User-agent
            navigator.cookieEnabled, // Checks whether cookies are enabled in browser
            navigator.appName, // Get the Name of Browser
            navigator.language,  // Get the Language of Browser
            navigator.appVersion,  // Get the Version of Browser
            navigator.platform  // Get the platform for which browser is compiled
        ],

        /* The array containing the browser info names */
        infoNames = [
                 "userAgent",
                 "cookiesEnabled",
                 "browserName",
                 "browserLang",
                 "browserVersion",
                 "browserPlatform"
        ];

    /* Creating the JSON object */
    for (var i = 0; i < info.length; i++) {
        if (i === info.length - 1) {
            json += '"' + infoNames[i] + '": "' + info[i] + '"';
        }
        else {
            json += '"' + infoNames[i] + '": "' + info[i] + '",';
        }
    };

    return json + "}]";
};