获取textarea文本框所选字符光标位置索引，以及选中的文本值；textarea高度自适应，随着内容增加高度增加；获取输入框中的光标位置

 　　　　　　　　$.fn.selection = function () {
                    var s, e, range, stored_range;
                    if (this[0].selectionStart == undefined) {
                        var selection = document.selection;
                        if (this[0].tagName.toLowerCase() != "textarea") {
                            var val = this.val();
                            range = selection.createRange().duplicate();
                            range.moveEnd("character", val.length);
                            s = (range.text == "" ? val.length : val.lastIndexOf(range.text));
                            range = selection.createRange().duplicate();
                            range.moveStart("character", -val.length);
                            e = range.text.length;
                        } else {
                            range = selection.createRange(),
                                stored_range = range.duplicate();
                            stored_range.moveToElementText(this[0]);
                            stored_range.setEndPoint(‘EndToEnd‘, range);
                            s = stored_range.text.length - range.text.length;
                            e = s + range.text.length;
                        }
                    } else {
                        s = this[0].selectionStart,
                            e = this[0].selectionEnd;
                    }
                    var te = this[0].value.substring(s, e);
                    return {start: s, end: e, text: te};
                };

                $.fn.autoHeight = function(){
                    return this.each(function(){
                        var $this = jQuery(this);
                        if( !$this.attr(‘_initAdjustHeight‘) ){
                            $this.attr(‘_initAdjustHeight‘, $this.outerHeight());
                        }
                        _adjustH(this).on(‘input‘, function(){
                            _adjustH(this);
                        });
                    });
                    /**
                     * 重置高度
                     * @param {Object} elem
                     */
                    function _adjustH(elem){
                        var $obj = jQuery(elem);
                        return $obj.css({height: $obj.attr(‘_initAdjustHeight‘), ‘overflow-y‘: ‘hidden‘})
                            .height( elem.scrollHeight );
                    }

                };

                $.fn.getCursorPosition = function () {
                    var el = $(this).get(0);
                    var pos = 0;
                    if (‘selectionStart‘ in el) {
                        pos = el.selectionStart;
                    } else if (‘selection‘ in document) {
                        el.focus();
                        var Sel = document.selection.createRange();
                        var SelLength = document.selection.createRange().text.length;
                        Sel.moveStart(‘character‘, -el.value.length);
                        pos = Sel.text.length - SelLength;
                    }
                    return pos;
                };