Echarts的tooltip加上单位并带着图例颜色

// tooltip的formatter
formatter: function (params) {
                        var relVal = params[0].name
                        for (var i = 0, l = params.length; i < l; i++) {
                            relVal += '<br/>' + params[i].marker + params[i].seriesName + ' : ' + params[i].value + '单位'
                        }
                        return relVal
                    }