目的要在新增的標記上都能順利跑出infowindow,後來發現它的content:"zzzzzzzzz"屬性是必要（？）參數,否則都沒用...

//初始化地圖
function initialize() {
    var haightAshbury = new google.maps.LatLng(37.7699298, -122.4469157);
    var mapOptions = {
      zoom: 12,
      center: haightAshbury,
      mapTypeId: google.maps.MapTypeId.TERRAIN
    };
    map = new google.maps.Map(document.getElementById("map_canvas"),
        mapOptions);
      
//畫線屬性  
    var polyOptions = {
    clickable:true,
    map:map,
    strokeColor: '#000000',
    strokeOpacity: 1.0,
    strokeWeight: 3
    }
//new Polyline（帶入上面屬性）
    poly = new google.maps.Polyline(polyOptions);
    
//按鍵事件
    google.maps.event.addListener(map, 'click', function(event) {
    addPoint(event.latLng); });
  }
  
  
  //增加標記的函數
  function addPoint(location) {
      var path=poly.getPath();    //沒寫在事件呼叫的函數裡好像沒作用,關網
                                        //畫線專用的陣列.getPath()    
      path.push(location);             //不是很懂這一段,只知push
      marker[i] = new google.maps.Marker({  //new 標記+屬性給一給
       position: location,
      title:"--"+i,
      map: map
    });
    
    //new 訊息框,content是必要屬性 幹,沒給內容就什麼都沒有
      infowindow=new google.maps.InfoWindow ({content: "contentString"});        
     infowindow.open(map,marker[i]); //紀錄指定標記和訊息窗的mach
    markersArray.push(marker); //擴充標記陣列（我多用一個"i"去記）
    i++;
     
  }