// Add printjs src
var script = document.createElement('script');
script.type = 'text/javascript';
script.src = 'https://printjs-4de6.kxcdn.com/print.min.js';
document.head.appendChild(script);
<script type=​"text/​javascript" src=​"https:​/​/​printjs-4de6.kxcdn.com/​print.min.js">​</script>​

// Get map canvas. TODO: Need to combine multiple canvas elements, not just first one for backgorund layers
let mapCanvas = document.querySelector("#farm-map-dashboard > div > div.ol-unselectable.ol-layers > div > canvas")
undefined

// Get data url from canvas, TODO: decide on format?
let data = mapCanvas.toDataURL('image/png')
undefined
let data = mapCanvas.toDataURL('image/jpeg')
undefined
let data = mapCanvas.toDataURL('image/webp')
undefined

// Create print dialog with printjs
printJS(data, 'image');