This is the core package that powers tileify-ags-proxy. If you want to create a slippy map tile service from your ArcGIS Server maps, you should probably head over there.
const TileifyAGS = require('tileify-ags');
const agsServerUrl = 'http:https://gis-web.co.union.nc.us/arcgis/rest/services/PWGIS_Web/Operational_Layers/MapServer';
const urlParamConfig = {
transparent: 'true',
layers: 'show:20',
};
const x = 144666;
const y = 207574;
const z = 19;
const pixelRatio = 2; // Optional: Use 2 to generate 512x512 tiles. Defaults to 1 (256x256 tiles).
const tiler = new TileifyAGS(agsServerUrl, urlParamConfig, pixelRatio);
const url = tiler.getTileUrl(x, y, z);
console.log(url);
// http:https://gis-web.co.union.nc.us/arcgis/rest/services/PWGIS_Web/Operational_Layers/MapServer/export?&bbox=-80.66574096679688%2C35.0530458107596%2C-80.66505432128906%2C35.053607911025594&bboxSR=4326&imageSR=3857&f=image&size=512%2C512&transparent=true&layers=show:20