How do I make npm pack "highcharts-export-server" wait for it to finish processing

Question

I am new to javascript and node.js and I am experimenting with "highcharts-export-server" where I am trying to get the chart as a base64 string. Here is my highchartstest.js file:

const chartExporter = require("highcharts-export-server");
var chartBase64 = null;
 function ProcessChart() {
    chartExporter.initPool(); // Initialize the exporter
    const chartDetails = {
        type: 'png',
        options: {
            title: {
                text: 'My Chart'
            },
            xAxis: {
                categories: ["Jan", "Feb", "Mar", "Apr", "Mar", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"]
            },
            series: [{
                    type: 'line',
                    data: [1, 3, 2, 4]
                },
                {
                    type: 'line',
                    data: [5, 3, 4, 2]
                }
            ]
        }
    };
    chartExporter.export(chartDetails, (err, res) => {
        chartBase64 = new Buffer.from(res.data, 'base64');  
        //console.log(chartBase64);
        chartExporter.killPool();
        return chartBase64;
    });
}
module.exports.ProcessChart = ProcessChart;

I have a another file called test.js with the following code:

var charts = require('./highchartsTest');
var chartBase = charts.ProcessChart();
console.log(chartBase);

If I run node test.js the result I get is undefined in the console. If I uncomment console.log(chartBase64); in highchartstest.js I can see that i get a result. Can someone please help me figure out how I can get this to wait for the processing to complete when I call var chartBase = charts.ProcessChart();

Answer 1

The undefined that you receive is not coming from the callback of the export function. The easiest way to receive a correct base64 string would be to add an argument to the ProcessChart function which is a callback that triggers after the killPool call. The code can look like this:

(highcharts-test.js)

const chartExporter = require('highcharts-export-server');

const ProcessChart = callback => {
    chartExporter.initPool(); // Initialize the exporter

    const chartDetails = {
        type: 'png',
        options: {
            title: {
                text: 'My Chart'
            },
            xAxis: {
                categories: ['Jan', 'Feb', 'Mar', 'Apr', 'Mar', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec']
            },
            series: [{
                type: 'line',
                data: [1, 3, 2, 4]
            }, {
                type: 'line',
                data: [5, 3, 4, 2]
            }]
        }
    };

    chartExporter.export(chartDetails, (err, res) => {
        if (res) {
            chartExporter.killPool();
            callback(res.data);
        }
    });
}

module.exports.ProcessChart = ProcessChart;

(test.js)

const exporter = require('./highcharts-test.js');

const ProcessChart = exporter.ProcessChart;

ProcessChart(base64 => {
    console.log(base64);
    process.exit();
});