如何使用JavaScript在移动Safari上设置缩放级别？

touchend

  <p id="tap">double tap to zoom</p>
  <input id="zoomWidth" type="text" value="400" />
  <p id="feedback"></p>

$(document).ready(function(){
  $('#tap').doubletap(
    // double tap handler
    function(e) {
      $('#feedback').addClass('red').html('double tap! Zoom width: ' + $('#zoomWidth').val());

      var zoomWidth = $('#zoomWidth').val();

      // zoom with the new width
      $('meta[name="viewport"]').attr('content', 'width=' + zoomWidth + ', user-scalable:no');

      $('#zoomWidth').val(parseInt(zoomWidth, 10) - 25);
    },

    // single tap handler
    function(e) {
      $('#feedback').removeClass('red').html('single tap! Zoom width: ' + $('#zoomWidth').val());
    },

    // double tap delay, default 500
    400
    );
});

<meta name="viewport" content="width=device-width; initial-scale=1.0; user-scalable:no;">