【备忘录】获取textarea光标位置

/**
* getCursorPosition Method
*
* Created by Blank Zheng on 2010/11/12.
* Copyright (c) 2010 PlanABC.net. All rights reserved.
*
* The copyrights embodied in the content of this file are licensed under the BSD (revised) open source license.
*/
function getCursorPosition(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(),
// Don't: oR = textarea.createTextRange()
oR = document.body.createTextRange();
oR.moveToElementText(textarea);

rangeData.text = oS.text;
rangeData.bookmark = oS.getBookmark();

// object.moveStart(sUnit [, iCount])
// Return Value: Integer that returns the number of units moved.
for (i = 0; oR.compareEndPoints('StartToStart', oS) < 0 && oS.moveStart("character", -1) !== 0; i ++) {
// Why? You can alert(textarea.value.length)
if (textarea.value.charAt(i) == '\n') {
i ++;
}
}
rangeData.start = i;
rangeData.end = rangeData.text.length + rangeData.start;
}

return rangeData;
}