if (navigator.userAgent.match(/iPhone/i) || navigator.userAgent.match(/iPad/i)) {
    var viewportmeta = document.querySelectorAll('meta[name="viewport"]')[0];
    if (viewportmeta) {
        viewportmeta.content = 'width=device-width, minimum-scale=1.0, maximum-scale=1.0';
        document.body.addEventListener('gesturestart', function() {
            viewportmeta.content = 'width=device-width, minimum-scale=0.25, maximum-scale=1.6';
        }, false);
    }
}