阻止双击放大ios10及以上meta标签的禁止操作会失效

<script>
window.onload = function() {
// 阻止双击放大ios10及以上meta标签的禁止操作会失效
var lastTouchEnd = 0;
document.addEventListener('touchstart', function(event) {
if (event.touches.length > 1) {
event.preventDefault();
}
});
document.addEventListener('touchend', function(event) {
var now = (new Date()).getTime();
if (now - lastTouchEnd <= 300) {
event.preventDefault();
}
lastTouchEnd = now;
}, false);

// 阻止双指放大无效
document.addEventListener('gesturestart', function(event) {
event.preventDefault();
});
}
</script>