echarts中formatter的值写成function,这个function可以是字符串吗?

描述:当前是关于Echarts图表中的 柱状图 示例。
 
            var weatherIcons = {
    'Sunny': './data/asset/img/weather/sunny_128.png',
    'Cloudy': './data/asset/img/weather/cloudy_128.png',
    'Showers': './data/asset/img/weather/showers_128.png'
};

var seriesLabel = {
    normal: {
        show: true,
        textBorderColor: '#333',
        textBorderWidth: 2
    }
}

option = {
    title: {
        text: 'Wheater Statistics'
    },
    tooltip: {
        trigger: 'axis',
        axisPointer: {
            type: 'shadow'
        },
        //在这里的function是字符串,结果显示的就是这串字符串,而没有运行该function
        formatter: function(params) {
            var tar;
            if (params[1].value != '-') {
                tar = params[1];
            } else {
                tar = params[0];
            }
            return tar.name + ' ' + tar.seriesName + ' : ' + tar.value;
        }





    },
    legend: {
        data: ['City Alpha', 'City Beta', 'City Gamma']
    },
    grid: {
        left: 100
    },
    toolbox: {
        show: true,
        feature: {
            saveAsImage: {}
        }
    },
    xAxis: {
        type: 'value',
        name: 'Days',
        axisLabel: {
            formatter: '{value}'
        }
    },
    yAxis: {
        type: 'category',
        inverse: true,
        data: ['Sunny', 'Cloudy', 'Showers'],
        axisLabel: {
            formatter: function(value) {
                return '{' + value + '| }\n{value|' + value + '}';
            },
            margin: 20,
            rich: {
                value: {
                    lineHeight: 30,
                    align: 'center'
                },
                Sunny: {
                    height: 40,
                    align: 'center',
                    backgroundColor: {
                        image: weatherIcons.Sunny
                    }
                },
                Cloudy: {
                    height: 40,
                    align: 'center',
                    backgroundColor: {
                        image: weatherIcons.Cloudy
                    }
                },
                Showers: {
                    height: 40,
                    align: 'center',
                    backgroundColor: {
                        image: weatherIcons.Showers
                    }
                }
            }
        }
    },
    series: [{
            name: 'City Alpha',
            type: 'bar',
            data: [165, 170, 30],
            label: seriesLabel,
            markPoint: {
                symbolSize: 1,
                symbolOffset: [0, '50%'],
                label: {
                    normal: {
                        formatter: '{a|{a}\n}{b|{b} }{c|{c}}',
                        backgroundColor: 'rgb(242,242,242)',
                        borderColor: '#aaa',
                        borderWidth: 1,
                        borderRadius: 4,
                        padding: [4, 10],
                        lineHeight: 26,
                        // shadowBlur: 5,
                        // shadowColor: '#000',
                        // shadowOffsetX: 0,
                        // shadowOffsetY: 1,
                        position: 'right',
                        distance: 20,
                        rich: {
                            a: {
                                align: 'center',
                                color: '#fff',
                                fontSize: 18,
                                textShadowBlur: 2,
                                textShadowColor: '#000',
                                textShadowOffsetX: 0,
                                textShadowOffsetY: 1,
                                textBorderColor: '#333',
                                textBorderWidth: 2
                            },
                            b: {
                                color: '#333'
                            },
                            c: {
                                color: '#ff8811',
                                textBorderColor: '#000',
                                textBorderWidth: 1,
                                fontSize: 22
                            }
                        }
                    }
                },
                data: [{
                        type: 'max',
                        name: 'max days: '
                    },
                    {
                        type: 'min',
                        name: 'min days: '
                    }
                ]
            }
        },
        {
            name: 'City Beta',
            type: 'bar',
            label: seriesLabel,
            data: [150, 105, 110]
        },
        {
            name: 'City Gamma',
            type: 'bar',
            label: seriesLabel,
            data: [220, 82, 63]
        }
    ]
};