Javascript 如何在c3.js中显示月和年的垂直刻度格式

我是为c3.js中的代码开发的，但是x轴中的tickformat显示了很多年和月，我无法显示特定的年和月，如何在c3.js中的d3.js库中使用任何参考网站。给定的代码是我开发的

    setTimeout(function () {
      chart = c3.generate({
        size:{height:500,width:600},
        padding:{left:100},
        data: {
          json: [{"key":[2000,0],"value":500},{"key":[2000,1],"value":600},{"key":[2000,2],"value":200},{"key":[2000,3],"value":100},{"key":[2000,4],"value":700},{"key":[2000,5],"value":200},{"key":[2000,6],"value":1940},{"key":[2000,7],"value":1562},{"key":[2000,8],"value":2163},{"key":[2000,9],"value":2148},{"key":[2000,10],"value":2228},{"key":[2000,11],"value":4081},{"key":[2001,0],"value":600},{"key":[2001,1],"value":1000},{"key":[2001,2],"value":5385},{"key":[2001,3],"value":9647},{"key":[2001,4],"value":6209},{"key":[2001,5],"value":6661},{"key":[2001,6],"value":26472},{"key":[2001,7],"value":11965},{"key":[2001,8],"value":13179},{"key":[2001,9],"value":14389},{"key":[2001,10],"value":63365},{"key":[2001,11],"value":17158},{"key":[2001,0],"value":10000}],

          names: {
            value: 'transactions',
            },

          keys: {
            x: 'key',
            value: ['value'],
          }

        },
        axis: {
          x: {
            type: 'category'

               },
           tick: {
      format: function (x) { return x.getFullYear(); }
    }

            },
          zoom: {
           enabled: true
           },

         grid: {
        x: {
            show: true
        },
        y: {
            show: true
        }
    },

        regions: [
        {axis: 'x', end: 1, class: 'regionX'},
        {axis: 'x', start: 2, end: 4, class: 'regionX'},
        {axis: 'x', start: 5, class: 'regionX'},
        {axis: 'y', end: 50, class: 'regionY'},
        {axis: 'y', start: 80, end: 140, class: 'regionY'},
        {axis: 'y', start: 400, class: 'regionY'},
        {axis: 'y2', end: 900, class: 'regionY2'},
        {axis: 'y2', start: 1150, end: 1250, class: 'regionY2'},
        {axis: 'y2', start: 1300, class: 'regionY2'},
    ]

      });
chart.transform('area', 'value');
chart.transform('area-spline');
    }, 2000);