echarts tooltip巧用

 tooltip : {
			        trigger: ‘item‘,
			        triggerOn: ‘click‘,
			        formatter:function(params,ticket,callback){			        	
			        	var res = ‘‘;
			        	for(var i = 0 ; i < _this.data.length; i++){
			        		if(params.name==_this.data[i].name){
			        			res = _this.data[i].rate;	
			        			_this.areaName = params.name;
			        			break;
			        		}
			        	}
			        	console.log(_this.areaName)
			        	return res;			        	
			        }
			    },