echart 饼图自定义百分比

tooltip : {
    trigger: 'item',
    formatter: function(a){
        return (a['name']+'<br/>'+a['value'] +':'+a['data'].datas[0]); //自定义百分比
    }
},
calculable: false,
series: [
    {
        name: '访问来源',
        type: 'pie',
        radius: '55%',
        center: ['50%', '60%'],
        data: [
            {value: 335, name: '直接访问', datas: ['11.20%']},
            {value: 310, name: '邮件营销', datas: ['31%']},
            {value: 234, name: '联盟广告', datas: ['24%']},
            {value: 135, name: '视频广告', datas: ['16%']},
            {value: 1548, name: '搜索引擎', datas: ['13.31%']},
        ]
    }
]