为什么在添加d3plus.js图表​​时无法加载脚本？

Question

我正在尝试使用d3plus.js将图表添加到我的网站。我收到以下错误消息：

Uncaught TypeError: Cannot read property 'buttons' of null

    at SVGGElement.<anonymous> (d3plus.js:23745)

    at SVGGElement.__onmousemove (d3.js:1120)

我尝试将脚本放置在页面的开头和页脚之后。

**head.php**

    <script src="../wp-content/themes/sage/bower_components/d3/d3.js"> </script>

    <script src="../wp-content/themes/sage/bower_components/d3plus/d3plus.js"></script>

**page.php**

    <div id="viz" width="1356" height="579"></div>

    <script>

    var data = [

      {"year": 1991, "name":"alpha", "value": 15},

      {"year": 1991, "name":"beta", "value": 10},

      {"year": 1991, "name":"gamma", "value": 5},

      {"year": 1991, "name":"delta", "value": 50},

      {"year": 1992, "name":"alpha", "value": 20},

      {"year": 1992, "name":"beta", "value": 10},

      {"year": 1992, "name":"gamma", "value": 10},

      {"year": 1992, "name":"delta", "value": 43},

      {"year": 1993, "name":"alpha", "value": 30},

      {"year": 1993, "name":"beta", "value": 40},

      {"year": 1993, "name":"gamma", "value": 20},

      {"year": 1993, "name":"delta", "value": 17},

      {"year": 1994, "name":"alpha", "value": 60},

      {"year": 1994, "name":"beta", "value": 60},

      {"year": 1994, "name":"gamma", "value": 25},

      {"year": 1994, "name":"delta", "value": 32}

    ]

    var visualization = d3plus.viz()

      .container("#viz")

      .data(data)

      .type("bar")

      .id("name")

      .height(300)

      .width(1100)

      .x("year")

      .y("value")

      .draw()

    </script>

鼠标悬停时，标签应显示在图表上，但出现错误消息：

Uncaught TypeError: Cannot read property 'buttons' of null

    at SVGGElement.<anonymous> (d3plus.js:23745)

    at SVGGElement.__onmousemove (d3.js:1120)