input 和 textarea 输入框最大文字限制插件

/* 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
 * vsync.design@gmail.com
*/
; 
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);