After echarts tooltip display value%

Requirements: Requirements echarts when the mouse hover can see behind the data show the percent sign (background data is already processed).

Renderings:

Code:

tooltip: {
          trigger: 'axis',
          formatter: function(params) {
            var result = params[0].name + "<br>";
            params.forEach(function(item) {
              if (item.value) {
                result += item.marker + " " + item.seriesName + " : " + item.value + "%</br>";
              } else {
                result += item.marker + " " + item.seriesName + " :  - </br>";
              }
            });
            return result;
          }
        },

PS: there will be some data has no value to undefined% show, if I am here to do a deal. If it helps you, trouble recommend it!