1. js部分 

 <script language="javascript">
                                                    
	                                                function setCursorPosition( index) {
	                                                	var elem = event.srcElement;
	                                                    var val = elem.value
	                                                    var len = val.length
	                                                    // 超過文字長度直接返回
	                                                    if (len < index) return
	                                                    setTimeout(function() {
	                                                        elem.focus()
	                                                        if (elem.setSelectionRange) { // 標準瀏覽器
	                                                            elem.setSelectionRange(index, index)   
	                                                        } else { // IE9-
	                                                            var range = elem.createTextRange()
	                                                            range.moveStart("character", -len)
	                                                            range.moveEnd("character", -len)
	                                                            range.moveStart("character", index)
	                                                            range.moveEnd("character", 0)
	                                                            range.select()
	                                                        }
	                                                    }, 10)
	                                                } 

                                                </script>
 

index 為游標的位置.

2. body部分

<div class="control-item">
                                                        <textarea rows="3"  ondblclick="setCursorPosition(0)"
                                                                
                                                                  style="font-size:12px; height:60px;"></textarea>
                                                    </div>