js或jquery在textarea光标位置后面添加文本

$.fn.extend({    
05        position:function( value ){    
06            var elem = this[0];    
07                if (elem&&(elem.tagName=="TEXTAREA"||elem.type.toLowerCase()=="text")) {    
08                   if($.browser.msie){    
09                           var rng;    
10                           if(elem.tagName == "TEXTAREA"){    
11                                rng = event.srcElement.createTextRange();    
12                                rng.moveToPoint(event.x,event.y);    
13                           }else{    
14                                rng = document.selection.createRange();    
15                           }    
16                           if( value === undefined ){    
17                             rng.moveStart("character",-event.srcElement.value.length);    
18                             return  rng.text.length;    
19                           }else if(typeof value === "number" ){    
20                             var index=this.position();    
21                             index>value?( rng.moveEnd("character",value-index)):(rng.moveStart("character",value-index))    
22                             rng.select();    
23                           }    
24                    }else{    
25                        if( value === undefined ){    
26                             return elem.selectionStart;    
27                           }else if(typeof value === "number" ){    
28                             elem.selectionEnd = value;    
29                             elem.selectionStart = value;    
30                           }    
31                    }    
32                }else{    
33                    if( value === undefined )    
34                       return undefined;    
35                }    
36        }    
37    })

引用：http://www.oschina.net/code/snippet_4873_3395