Worker urls are resolved relative to the HTML not the script, here's how to write a script that can be called as js/scriptname.js and as scripts/scriptname.js. Still has to be same domain.

scriptWithWorker.js

if (typeof document === "undefined") {(function(self){
	self.onmessage=function(e){
		/*
		worker stuff
		*/
	}
})(self)} else {(function(exports){
	"use strict";
	function getPath(){
		var scripts = document.getElementsByTagName("script");
		var len = scripts.length;
		var i = 0;
 		while(i<len){
/*  change  --------> */if(/scriptWithWorker(\.min)?\.js/.test(scripts[i].src)){
				return scripts[i].src;
 			}
			i++;
		}
	}
	var worker = new Worker(getPath());
	/*
	none worker code
	*/
})(window)};