input 和 textarea 输入框最大文字限制的jquery插件

/* input 和 textarea 最大文字限定插件 
* 修改版, 一个中文表示1一个字, 一个英文半个字; 
* TextLimit - jQuery plugin for counting and limiting characters for input and textarea fields 
* 
* pass '-1' as speed if you don't want the char-deletion effect. (don't just put 0) 
* Example: jQuery("Textarea").textlimit('span.counter',256) 
* 
* $Version: 2009.07.25 +r2 
* Copyright (c) 2009 Yair Even-Or 
* [e-mail] 
*/ String.prototype.getBytes = function () { 
var cArr = this.match(/[^\x00-\xff]/ig); 
return this.length + (cArr == null ? 0 : cArr.length); 
}; 
(function(jQuery) { 
jQuery.fn.textlimit=function(counter_el, thelimit, speed) { 
var charDelSpeed = speed || 15; 
var toggleCharDel = speed != -1; 
var toggleTrim = true; 
var that = this[0]; 
var isCtrl = false; 
updateCounter(); 
function updateCounter(){ 
if(typeof that == "object") 
jQuery(counter_el).text(thelimit - Math.ceil(that.value.getBytes()/2)); 
}; 
this.keydown (function(e){ 
if(e.which == 17) isCtrl = true; 
var ctrl_a = (e.which == 65 && isCtrl == true) ? true : false; // detect and allow CTRL + A selects all. 
var ctrl_v = (e.which == 86 && isCtrl == true) ? true : false; // detect and allow CTRL + V paste. 
// 8 is 'backspace' and 46 is 'delete' 
if( this.value.length >= thelimit && e.which != '8' && e.which != '46' && ctrl_a == false && ctrl_v == false) 
e.preventDefault(); 
}) 
.keyup (function(e){ 
updateCounter(); 
if(e.which == 17) 
isCtrl=false; 
if( this.value.length >= thelimit && toggleTrim ){ 
if(toggleCharDel){ 
// first, trim the text a bit so the char trimming won't take forever 
// Also check if there are more than 10 extra chars, then trim. just in case. 
if ( (this.value.length - thelimit) > 10 ) 
that.value = that.value.substr(0,thelimit+100); 
var init = setInterval 
( 
function(){ 
if( that.value.length <= thelimit ){ 
init = clearInterval(init); updateCounter() 
} 
else{ 
// deleting extra chars (one by one) 
that.value = that.value.substring(0,that.value.length-1); jQuery(counter_el).text(Math.ceil(that.value.getBytes()/2)); 
} 
} ,charDelSpeed 
); 
} 
else this.value = that.value.substr(0,thelimit); 
} 
}); 
}; 
})(jQuery);