Chartjs-How to use plugin in chartjs-node?

I faced this issue as well, I managed to fix it like this:
This is an example for the chartjs-plugin-annotation

What I forgot was to register the plugin in the beforeDraw event

const ChartjsNode = require('chartjs-node');
const ChartjsAnnotation = require('chartjs-plugin-annotation');

var chartNode = new ChartjsNode(width, height);
chartNode.on('beforeDraw', function (Chartjs) {

    // Register the annotation plugin
    Chartjs.plugins.register( ChartjsAnnotation );
});

chartNode.drawChart( <your_chartjs_configuration> )
.then( function(){
    // Save as testimage.png
    chartNode.writeImageToFile('image/png', './testimage.png'); 
});

And your configuration (example):

type: 'line',
data: {
   ...
},
options: {
    ...
    annotation: {
        annotations: [{
            value: 100,
            type: 'line',
            mode: 'horizontal',
            scaleID: 'y-axis-0',
            borderColor: '#D2DAE2',
            borderWidth: 1,
            borderDash: [2, 2],
            label: {
                content: 'Value 1'
            }
        }, {
            value: 50
            type: 'line',
            mode: 'horizontal',
            scaleID: 'y-axis-0',
            borderColor: '#D2DAE2',
            borderWidth: 1,
            borderDash: [2, 2],
            value: 500,
            label: {
                content: 'Value 2'
             }
        }]
    }