js兑现输入框焦点中插入文字

js实现输入框焦点中插入文字

var focus_tag = { first:function(area){           area.focus();           if (area == null) {               area = event.srcElement;           }           if(document.selection){               var rtextRange = area.createTextRange();               rtextRange.moveStart('character', area.value.length);               rtextRange.collapse(true);               rtextRange.select();           }     },getCursorPosition:function(textarea) {             var rangeData = {text: "", start: 0, end: 0 };             textarea.focus();         if (textarea.setSelectionRange) { // W3C             rangeData.start= textarea.selectionStart;             rangeData.end = textarea.selectionEnd;             rangeData.text = (rangeData.start != rangeData.end) ? textarea.value.substring(rangeData.start, rangeData.end): "";         } else if (document.selection) { // IE             var i,                 oS = document.selection.createRange(),                 oR = document.body.createTextRange();             oR.moveToElementText(textarea);                      rangeData.text = oS.text;             rangeData.bookmark = oS.getBookmark();             for (i = 0; oR.compareEndPoints('StartToStart', oS) < 0 && oS.moveStart("character", -1) !== 0; i ++) {                 if (textarea.value.charAt(i) == '\n') {                     i ++;                 }             }             rangeData.start = i;             rangeData.end = rangeData.text.length + rangeData.start;         }                  return rangeData;     }, setCursorPosition:function(textarea, rangeData) {         if(!rangeData) {             alert("You must get cursor position first.");         }         if (textarea.setSelectionRange ) { // W3C             textarea.focus();             textarea.setSelectionRange(rangeData.start, rangeData.end);         } else if (textarea.createTextRange) { // IE             var oR = textarea.createTextRange();             if(textarea.value.length === rangeData.start) {                 oR.collapse(false);                 oR.select();             } else {                 oR.moveToBookmark(rangeData.bookmark);                 oR.select();             }         }     },add:function (textarea, rangeData,text) {         var oValue, nValue, oR, sR, nStart, nEnd, st;         this.setCursorPosition(textarea, rangeData);         if (textarea.setSelectionRange) { // W3C             oValue = textarea.value;             nValue = oValue.substring(0, rangeData.start) + text + oValue.substring(rangeData.end);             nStart = nEnd = rangeData.start + text.length;             st = textarea.scrollTop;             textarea.value = nValue;             if(textarea.scrollTop != st) {                 textarea.scrollTop = st;             }             textarea.setSelectionRange(nStart, nEnd);         } else if (textarea.createTextRange) { // IE             sR = document.selection.createRange();             sR.text = text;             sR.setEndPoint('StartToEnd', sR);             sR.select();         }     } }