问新人求解。。。？

(function($) {

 $.textMetrics = function(el) {

  var h = 0, w = 0;

  var div = document.createElement('div');

  document.body.appendChild(div);

  $(div).css({

   position: 'absolute',

   left: -1000,

   top: -1000,

   display: 'none'

  });

  $(div).html($(el).html());

  var styles = ['font-size','font-style', 'font-weight', 'font-family','line-height', 'text-transform', 'letter-spacing'];

  $(styles).each(function() {

   var s = this.toString();

   $(div).css(s, $(el).css(s));

  });

  h = $(div).outerHeight();

  w = $(div).outerWidth();

  $(div).remove();

  var ret = {

   height: h,

   width: w

  };

  return ret;

 }

})(jQuery);

<div id="Test">

    abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ

</div>

CSS：

{

    position: absolute;

    visibility: hidden;

    height: auto;

    width: auto;

    white-space: nowrap; /* Thanks to Herb Caudill comment */

}

var test = document.getElementById("Test");

test.style.fontSize = fontSize;

var height = (test.clientHeight + 1) + "px";

var width = (test.clientWidth + 1) + "px";