prevent iOS from zooming on doubletap (pure JS)

no_doubletap_zooming.js

var doubleTouchStartTimestamp = 0;
$(document).bind("touchstart", function(event){
    var now = +(new Date());
    if (doubleTouchStartTimestamp + 500 > now){
        event.preventDefault();
    };
    doubleTouchStartTimestamp = now;
});