用expressjs在highcharts-export-server中出错

Question

我正在尝试创建一个REST API，以使用node和express导出Highcharts。下面是我的代码，

var express = require('express');
var path = require('path');
var bodyParser = require("body-parser");
const chartExporter = require("highcharts-export-server");

var app = express();
app.use(bodyParser.json());

var port = 1200;

app.post('/chart', function(req, res){
    console.log("Json Body from the post request\n", req.body);
    chartExporter.initPool();
    chartExporter.export(res.body, function(error, response){
        console.log("Error from the function", error);
        var imageb64 = response.data;
        console.log("Image From the exporter\n", imageb64);
    });
    chartExporter.killPool();
    console.log("\nPool Killed");
    return "Server Returns successfully!";
});

module.exports = app;

图表选项在下面，作为API的主体传递，

{
   "type": "png",
   "options": {
       "chart": {
           "type": "pie"
       },
       "title": {
           "text": "Heading of Chart"
       },
       "plotOptions": {
           "pie": {
               "dataLabels": {
                   "enabled": true,
                   "format": "<b>{point.name}</b>: {point.y}"
               }
           }
       },
       "series": [
           {
               "data": [
                   {
                       "name": "a",
                       "y": 100
                   },
                   {
                       "name": "b",
                       "y": 20
                   },
                   {
                       "name": "c",
                       "y": 50
                   }
               ]
           }
       ]
   }
}

如果我运行API，则会收到以下错误消息

TypeError: Cannot read property 'svg' of undefined
    at Object.module.exports [as export] (D:\Dev\hc-export-server\node_modules\highcharts-export-server\lib\chart.js:270:23)
    at D:\Dev\hc-export-server\server.js:60:22
    at Layer.handle [as handle_request] (D:\Dev\hc-export-server\node_modules\express\lib\router\layer.js:95:5)
    at next (D:\Dev\hc-export-server\node_modules\express\lib\router\route.js:137:13)
    at Route.dispatch (D:\Dev\hc-export-server\node_modules\express\lib\router\route.js:112:3)
    at Layer.handle [as handle_request] (D:\Dev\hc-export-server\node_modules\express\lib\router\layer.js:95:5)
    at D:\Dev\hc-export-server\node_modules\express\lib\router\index.js:281:22
    at Function.process_params (D:\Dev\hc-export-server\node_modules\express\lib\router\index.js:335:12)
    at next (D:\Dev\hc-export-server\node_modules\express\lib\router\index.js:275:10)
    at D:\Dev\hc-export-server\node_modules\body-parser\lib\read.js:130:5

但是，如果我在API之外单独运行同一组代码（让我们在同一文件中说），那么我将从导出器函数获得响应。像下面。响应将在终端中打印出来。

var express = require('express');
var path = require('path');
var bodyParser = require("body-parser");
const chartExporter = require("highcharts-export-server");

var app = express();
app.use(bodyParser.json());

var port = 1200;

const chartDetails = {
   "type": "png",
   "options": {
       "chart": {
           "type": "pie"
       },
       "title": {
           "text": "Heading of Chart"
       },
       "plotOptions": {
           "pie": {
               "dataLabels": {
                   "enabled": true,
                   "format": "<b>{point.name}</b>: {point.y}"
               }
           }
       },
       "series": [
           {
               "data": [
                   {
                       "name": "a",
                       "y": 100
                   },
                   {
                       "name": "b",
                       "y": 20
                   },
                   {
                       "name": "c",
                       "y": 50
                   }
               ]
           }
       ]
   }
};
chartExporter.initPool();
chartExporter.export(chartDetails, function(error, response){
        var imageb64 = response.data;
        console.log("Image From the exporter\n", imageb64);
    });
app.listen(port, function(){
    console.log("Server started at port ",  port);
});

app.post('/chart', function(req, res){
    console.log("Json Body from the post request\n", req.body);
    chartExporter.initPool();
    chartExporter.export(res.body, function(error, response){
        console.log("Error from the function", error);
        var imageb64 = response.data;
        console.log("Image From the exporter\n", imageb64);
    });
    chartExporter.killPool();
    console.log("\nPool Killed");
    return "Server Returns successfully!";
});

module.exports = app;

如何使其在REST API中起作用？感谢任何帮助。谢谢