function NullRenderer( options ){ this.options = options; this.notifications = 0; // for testing } let noop = function(){}; let throwImgErr = function(){ throw new Error('A headless instance can not render images'); }; NullRenderer.prototype = { recalculateRenderedStyle: noop, notify: function(){ this.notifications++; }, init: noop, isHeadless: function(){ return true; }, png: throwImgErr, jpg: throwImgErr }; export default NullRenderer;