Javascript CanvasJS-条带线不显示

我正试图为弗雷德家在美国每月的房屋供应量编制一张图表。我已经能够使用Canvas.js来显示数据，但我似乎无法让条带线工作——我试图为每次衰退显示一条垂直条带线，但当我添加代码时，什么也没有显示，我正在遵循Canvas.js文档

jQuery.getJSON("h/data/monthlySupplyHousesUS.json", function(results) {  
    $.each(results.dataset.data, function(key, value){
        twoPoints.push({x: new Date(value[0]), y: parseFloat(value[1])});
    });
    var chart = new CanvasJS.Chart("monthlySupplyHousesUSChart",{
        title:{
            text:"Monthly Supply of Houses in United States"
        },
        axisX:{
            valueFormatString: "YYYY-MM",
            interval: 1,
            stripLines:[
                {
                    startValue:2007-01,
                    endValue:2009-01,                
                    color:"#d8d8d8",
                }
            ]                   
        },
        axisY: {
            title: "Supply"
        },
        toolTip: {
            shared: true
        },
        data: [{
            name: "Supply",
                showInLegend: true,
            legendText: "Index",
            type: "line",
            xValueFormatString: "YYYY-MM-DD",
            dataPoints : twoPoints
        }]
    });
    chart.render();
});

JSON看起来像：

{
  "dataset": {
    "id": 123643,
    "dataset_code": "MSACSR",
    "database_code": "FRED",
    "name": "Monthly Supply of Houses in the United States",
    "description": "Months' Supply Seasonally Adjusted, The months' supply is the ratio of houses for sale to houses sold. This statistic provides an indication of the size of the for sale inventory in relation to the number of houses currently being sold. The months' supply indicates how long  the current for sale inventory would last given the current sales rate if no additional new houses were built. ",
    "refreshed_at": "2018-06-25T23:28:04.022Z",
    "newest_available_date": "2018-05-01",
    "oldest_available_date": "1963-01-01",
    "column_names": ["Date", "Value"],
    "frequency": "monthly",
    "type": "Time Series",
    "premium": false,
    "limit": null,
    "transform": null,
    "column_index": null,
    "start_date": "1963-01-01",
    "end_date": "2018-05-01",
    "data": [
        ["2018-05-01", 5.2],
        ["2018-04-01", 5.5],
        ["2018-03-01", 5.3],
        ["2018-02-01", 5.4],
        ["2018-01-01", 5.6],
        ["2017-12-01", 5.5],
        ["2017-11-01", 4.9],
        ["2017-10-01", 5.6],
        ["2017-09-01", 5.3],
        ["2017-08-01", 6.0],
        ["2017-07-01", 6.0],
        ["2017-06-01", 5.3],
        ["2017-05-01", 5.4],
        ["2017-04-01", 5.4],
        ["2017-03-01", 5.0],
        ["2017-02-01", 5.1],
        ["2017-01-01", 5.3],
        ["2016-12-01", 5.6],
        ["2016-11-01", 5.3],
        ["2016-10-01", 5.2],
        ["2016-09-01", 5.2],
        ["2016-08-01", 5.0],
        ["2016-07-01", 4.5],
        ["2016-06-01", 5.2],
        ["2016-05-01", 5.2],
        ["2016-04-01", 5.1],
        ["2016-03-01", 5.4],
        ["2016-02-01", 5.4],
        ["2016-01-01", 5.5],
        ["2015-12-01", 5.2],
        ["2015-11-01", 5.5],
     ]
   }
 }  

---

由于x值是日期时间，所以带状线值也应作为日期时间给出

axisX:{
    valueFormatString: "YYYY-MM",
    interval: 1,
    stripLines:[
        {
            startValue: new Date("2007-01-01"),
            endValue:new Date("2009-01-01"),
            color:"#d8d8d8",
        }
    ]                   
},