echarts柱状图 渐变色

效果图： 

var xAxisData = []; var data = []; for (var i = 9; i < 16; i++) { xAxisData.push('5月' + i + '日'); data.push(Math.round(Math.random() * 500) + 200); } option = { title: { text: '柱状图示例', subtext: 'https://segmentfault.com/q/1010000005137138', sublink: 'https://segmentfault.com/q/1010000005137138' }, xAxis: [{ data: xAxisData.map(function(x){ if(x == "5月11日")return " "; return x; }), axisLabel: { textStyle: { color: '#03a9f4' } }, splitLine: { show: false } }, { // 辅助 x 轴 show: false, data: xAxisData.map(function(x){ if(x == "5月11日")return " "; return x; }) }], yAxis: { max: 1000, axisLine: { show: false } }, series: [ { // 辅助系列 type : 'bar', silent : true, xAxisIndex : 1, itemStyle : { normal : { barBorderRadius: 20, color : '#ddd' } }, barWidth: 20, data: data.map(function (val) { return 1000; }) }, { type: 'bar', data: data, barWidth: 20, itemStyle: { normal: { barBorderRadius: 20, color: new echarts.graphic.LinearGradient(0, 0, 0, 1, [{ offset: 0, color: '#99d9ea' }, { offset: 1, color: '#3fa7dc' }]), shadowColor: 'rgba(0, 0, 0, 0.4)', shadowBlur: 20 } } } ] };