微信小程序上 map 设置 scale 无效，求指点

    <view class="h100 w100">  
        <!-- <view class="h100 w100" v-if="Platform==='H5'" id="indexMap"> </view> -->  
        <map    
        id="indexMap"   
        ref='indexMap1'   
        @regionchange='changeEvent'   
        :show-location='showLocation'   
        style="width: 100%; height: 100%;"   
        :latitude="locationInfo.lat"   
        :longitude="locationInfo.lng"   
        :markers ='markers'  
        :scale="scale"  
        :min-scale='3'  
        :max-scale='18'  
        @callouttap='callouttap'  
        @updated ='mapUpdated'  
        >  
        </map>  
    </view>  

    uni.$on('moveStart',res=>{  
                console.log('map moveStart: ',res.name);  
                    console.log('this.mapContext: ', this.mapContext);  
                    this.scale = 18  
                    this.mapContext&&this.mapContext.moveToLocation({  
                        latitude:Number(res.lat),  
                        longitude:Number(res.lng),  
                        success:res=> {    

                            console.log('moveToLocation222',res)    
                        }  
                    })  

            })