using Detectizr

var browser_ok = {
    firefox: 17,
    ie: 8,
    chrome: 23,
    safari: 4
};

var browser_good = {
    firefox: 20,
    ie: 9,
    chrome: 27,
    safari: 5
};

console.log(Detectizr);


//http://stackoverflow.com/questions/921789/how-to-loop-through-javascript-object-literal-with-objects-as-members

var show_error = false;
for (var key in browser_ok) {
    value = browser_ok[key];
    browser = Detectizr.browser;
    
    if ((browser.name === key) && (parseInt(browser.major) < value)){
        show_error = true;
    }
}

var show_warning = false;
for (var key in browser_good) {
    value = browser_good[key];
    browser = Detectizr.browser;
    
    if ((browser.name === key) && (parseInt(browser.major) < value)){
        show_warning = true;
    }
}

if (show_error){
    alert('Your browser is too old. So do you, old man!');
} else if (show_warning){
    alert('Your browser needs an update soon.');
}