我正在添加另一个答案，因为我的上一个答案已经变得有些史诗了。

这是我认为最好的版本：它采用了 bobince 的方法（在我的第一个答案的评论中提到）并修复了我不喜欢它的两件事，首先是它依赖于文本区域之外的 TextRanges （从而损害性能），其次是必须为字符数选择一个巨大的数字来移动范围边界的肮脏。

function getSelection(el) {
    var start = 0, end = 0, normalizedValue, range,
        textInputRange, len, endRange;

    if (typeof el.selectionStart == "number" && typeof el.selectionEnd == "number") {
        start = el.selectionStart;
        end = el.selectionEnd;
    } else {
        range = document.selection.createRange();

        if (range && range.parentElement() == el) {
            len = el.value.length;
            normalizedValue = el.value.replace(/\r\n/g, "\n");

            // Create a working TextRange that lives only in the input
            textInputRange = el.createTextRange();
            textInputRange.moveToBookmark(range.getBookmark());

            // Check if the start and end of the selection are at the very end
            // of the input, since moveStart/moveEnd doesn't return what we want
            // in those cases
            endRange = el.createTextRange();
            endRange.collapse(false);

            if (textInputRange.compareEndPoints("StartToEnd", endRange) > -1) {
                start = end = len;
            } else {
                start = -textInputRange.moveStart("character", -len);
                start += normalizedValue.slice(0, start).split("\n").length - 1;

                if (textInputRange.compareEndPoints("EndToEnd", endRange) > -1) {
                    end = len;
                } else {
                    end = -textInputRange.moveEnd("character", -len);
                    end += normalizedValue.slice(0, end).split("\n").length - 1;
                }
            }
        }
    }

    return {
        start: start,
        end: end
    };
}

var el = document.getElementById("your_textarea");
var sel = getSelection(el);
alert(sel.start + ", " + sel.end);

负数以百万计的举动似乎完美无缺。

这是我的结果：

var sel=document.selection.createRange();
var temp=sel.duplicate();
temp.moveToElementText(textarea);
var basepos=-temp.moveStart('character', -10000000);

this.m_selectionStart = -sel.moveStart('character', -10000000)-basepos;
this.m_selectionEnd = -sel.moveEnd('character', -10000000)-basepos;
this.m_text=textarea.value.replace(/\r\n/gm,"\n");

谢谢 bobince - 当它只是一个评论时，我怎么能投票给你的答案:(

一个 jquery 插件，用于在文本区域中获取选择索引的开始和结束。上面的javascript代码不适用于IE7和IE8并且给出了非常不一致的结果，所以我写了这个小的jquery插件。允许临时保存选择的开始和结束索引，并在以后突出显示选择。

一个工作示例和简短版本在这里：http : //jsfiddle.net/hYuzk/3/

带有评论等的更详细版本在这里：http : //jsfiddle.net/hYuzk/4/

        // Cross browser plugins to set or get selection/caret position in textarea, input fields etc for IE7,IE8,IE9, FF, Chrome, Safari etc 
        $.fn.extend({ 
            // Gets or sets a selection or caret position in textarea, input field etc. 
            // Usage Example: select text from index 2 to 5 --> $('#myTextArea').caretSelection({start: 2, end: 5}); 
            //                get selected text or caret position --> $('#myTextArea').caretSelection(); 
            //                if start and end positions are the same, caret position will be set instead o fmaking a selection 
            caretSelection : function(options) 
            { 
            if(options && !isNaN(options.start) && !isNaN(options.end)) 
            { 
            this.setCaretSelection(options); 
            } 
            else 
            { 
            return this.getCaretSelection(); 
            } 
            }, 
            setCaretSelection : function(options) 
            { 
            var inp = this[0]; 
            if(inp.createTextRange) 
            { 
            var selRange = inp.createTextRange(); 
            selRange.collapse(true); 
            selRange.moveStart('character', options.start); 
            selRange.moveEnd('character',options.end - options.start); 
            selRange.select(); 
            } 
            else if(inp.setSelectionRange) 
            { 
            inp.focus(); 
            inp.setSelectionRange(options.start, options.end); 
            } 
            }, 
            getCaretSelection: function() 
            { 
            var inp = this[0], start = 0, end = 0; 
            if(!isNaN(inp.selectionStart)) 
            { 
            start = inp.selectionStart; 
            end = inp.selectionEnd; 
            } 
            else if( inp.createTextRange ) 
            { 
            var inpTxtLen = inp.value.length, jqueryTxtLen = this.val().length; 
            var inpRange = inp.createTextRange(), collapsedRange = inp.createTextRange(); 

            inpRange.moveToBookmark(document.selection.createRange().getBookmark()); 
            collapsedRange.collapse(false); 

            start = inpRange.compareEndPoints('StartToEnd', collapsedRange) > -1 ? jqueryTxtLen : inpRange.moveStart('character', -inpTxtLen); 
            end = inpRange.compareEndPoints('EndToEnd', collapsedRange) > -1 ? jqueryTxtLen : inpRange.moveEnd('character', -inpTxtLen); 
            } 
            return {start: Math.abs(start), end: Math.abs(end)}; 

            }, 
            // Usage: $('#txtArea').replaceCaretSelection({start: startIndex, end: endIndex, text: 'text to replace with', insPos: 'before|after|select'}) 
            // Options     start: start index of the text to be replaced 
            //               end: end index of the text to be replaced 
            //              text: text to replace the selection with 
            //            insPos: indicates whether to place the caret 'before' or 'after' the replacement text, 'select' will select the replacement text 

            replaceCaretSelection: function(options) 
            { 
            var pos = this.caretSelection(); 
            this.val( this.val().substring(0,pos.start) + options.text + this.val().substring(pos.end) ); 
            if(options.insPos == 'before') 
            { 
            this.caretSelection({start: pos.start, end: pos.start}); 
            } 
            else if( options.insPos == 'after' ) 
            { 
            this.caretSelection({start: pos.start + options.text.length, end: pos.start + options.text.length}); 
            } 
            else if( options.insPos == 'select' ) 
            { 
            this.caretSelection({start: pos.start, end: pos.start + options.text.length}); 
            } 
            } 
        }); 

注意请参阅我的其他答案以获取我可以提供的最佳解决方案。我把这个留在这里作为背景。

我遇到了这个问题并编写了以下适用于所有情况的内容。在IE中它确实使用了您建议的在选择边界处临时插入一个字符的方法，然后使用document.execCommand("undo")删除插入的字符并防止插入保留在撤消堆栈中。我很确定没有更简单的方法。令人高兴的是，IE 9 将支持selectionStart和selectionEnd属性。

function getSelectionBoundary(el, isStart) {
    var property = isStart ? "selectionStart" : "selectionEnd";
    var originalValue, textInputRange, precedingRange, pos, bookmark;

    if (typeof el[property] == "number") {
        return el[property];
    } else if (document.selection && document.selection.createRange) {
        el.focus();
        var range = document.selection.createRange();

        if (range) {
            range.collapse(!!isStart);

            originalValue = el.value;
            textInputRange = el.createTextRange();
            precedingRange = textInputRange.duplicate();
            pos = 0;

            if (originalValue.indexOf("\r\n") > -1) {
                // Trickier case where input value contains line breaks

                // Insert a character in the text input range and use that as
                // a marker
                range.text = " ";
                bookmark = range.getBookmark();
                textInputRange.moveToBookmark(bookmark);
                precedingRange.setEndPoint("EndToStart", textInputRange);
                pos = precedingRange.text.length - 1;

                // Executing an undo command to delete the character inserted
                // prevents this method adding to the undo stack. This trick
                // came from a user called Trenda on MSDN:
                // http://msdn.microsoft.com/en-us/library/ms534676%28VS.85%29.aspx
                document.execCommand("undo");
            } else {
                // Easier case where input value contains no line breaks
                bookmark = range.getBookmark();
                textInputRange.moveToBookmark(bookmark);
                precedingRange.setEndPoint("EndToStart", textInputRange);
                pos = precedingRange.text.length;
            }
            return pos;
        }
    }
    return 0;
}

var el = document.getElementById("your_textarea");
var startPos = getSelectionBoundary(el, true);
var endPos = getSelectionBoundary(el, false);
alert(startPos + ", " + endPos);

更新

根据 bobince 在评论中建议的方法，我创建了以下内容，这似乎运行良好。一些注意事项：

1. bobince 的方法更简单、更短。
2. 我的方法是侵入性的：它在恢复这些更改之前对输入的值进行更改，尽管没有明显的效果。
3. 我的方法的优点是将所有操作都保留在输入中。bobince 的方法依赖于创建从正文开始到当前选择的范围。
4. 3. 的结果是 bobince 的性能随文档中输入位置的不同而变化，而我的则不然。我的简单测试表明，当输入接近文档开头时，bobince 的方法要快得多。当输入位于大量 HTML 之后时，我的方法会更快。

function getSelection(el) {
    var start = 0, end = 0, normalizedValue, textInputRange, elStart;
    var range = document.selection.createRange();
    var bigNum = -1e8;

    if (range && range.parentElement() == el) {
        normalizedValue = el.value.replace(/\r\n/g, "\n");

        start = -range.moveStart("character", bigNum);
        end = -range.moveEnd("character", bigNum);

        textInputRange = el.createTextRange();
        range.moveToBookmark(textInputRange.getBookmark());
        elStart = range.moveStart("character", bigNum);

        // Adjust the position to be relative to the start of the input
        start += elStart;
        end += elStart;

        // Correct for line breaks so that offsets are relative to the
        // actual value of the input
        start += normalizedValue.slice(0, start).split("\n").length - 1;
        end += normalizedValue.slice(0, end).split("\n").length - 1;
    }
    return {
        start: start,
        end: end
    };
}

var el = document.getElementById("your_textarea");
var sel = getSelection(el);
alert(sel.start + ", " + sel.end);