Safari iPad : prevent zoom on double-tap

I'm creating a site on Safari for iPad. I need to prevent the zoom on double-tapping event but I have two problems:

• a double tap doesn’t generate any events, so I can't use "event.preventDefault();"
• I need to do this only when some conditions are fulfilled, so I can't use the tag "<meta name = "viewport" content = "user-scalable = no">"... If I did that, users could never zoom on my page.

How can I fix these problems?

Here's a jQuery plugin I wrote for the same purpose - selectively disabling double-tap zoom on given page elements (in my case, navigation buttons to flip pages) I want to respond to every tap (including double-tap) as a normal click event, with no iOS "touch magic".

To use it, just run something like $('.prev,.next').nodoubletapzoom(); on the elements you care for. (Edit: now also ignores pinches)

// jQuery no-double-tap-zoom plugin

// Triple-licensed: Public Domain, MIT and WTFPL license - share and enjoy!

(function($) {
  var IS_IOS = /iphone|ipad/i.test(navigator.userAgent);
  $.fn.nodoubletapzoom = function() {
    if (IS_IOS)
      $(this).bind('touchstart', function preventZoom(e) {
        var t2 = e.timeStamp
          , t1 = $(this).data('lastTouch') || t2
          , dt = t2 - t1
          , fingers = e.originalEvent.touches.length;
        $(this).data('lastTouch', t2);
        if (!dt || dt > 500 || fingers > 1) return; // not double-tap

        e.preventDefault(); // double tap - prevent the zoom
        // also synthesize click events we just swallowed up
        $(this).trigger('click').trigger('click');
      });
  };
})(jQuery);

Mobile Safari does not support the javascript ondblclick event. It's interpreted by Safari as a "zoom".

Raul Sanchez has posted a potential solution: http://appcropolis.com/implementing-doubletap-on-iphones-and-ipads/

try this modified code. It should work for both android and IOS devices

(function($) {
$.fn.nodoubletapzoom = function() {
    $(this).bind('touchstart', function preventZoom(e){
        var t2 = e.timeStamp;
        var t1 = $(this).data('lastTouch') || t2;
        var dt = t2 - t1;
        var fingers = e.originalEvent.touches.length;
        $(this).data('lastTouch', t2);
        if (!dt || dt > 500 || fingers > 1){
            return; // not double-tap
        }
        e.preventDefault(); // double tap - prevent the zoom
        // also synthesize click events we just swallowed up
        $(e.target).trigger('click');
    });
};
})(jQuery);

Then apply the nodoubletapzoom() to the body tag

$("body").nodoubletapzoom();