Creating disposable threads in javascript.

thread.js

// Call the function with at least one parameter. 
// The last parameter must be a function that will run on it's own thread
// Any params that are passed to Thread() will be available in the thread function
// The last param of the thread function must be 


function Thread(){
	return new Promise((resolve, reject)=>{
		var args = Array.from(arguments);
		var func = args.pop();
		if(typeof func !== "function") throw new Error("Invalid function");
		var fstr = func.toString();
		var mainBody = fstr.substring(fstr.indexOf("{")+1, fstr.lastIndexOf("}"));
		var paramNames = fstr.substring(fstr.indexOf("(")+1, fstr.indexOf(")")).split(",").map(p=>p.trim());
		var doneFunct = paramNames.pop();
		if(paramNames.length !== args.length) throw new Error("Invalid number of arguments.");
		var workerStr = `var ${doneFunct} = function(){
			var args = Array.from(arguments);
			postMessage(args);
		};
		self.onmessage = function(d){
			var [${paramNames.join(", ")}] = d.data;
			${mainBody}
		};`;
		var blob = new Blob([workerStr], {type: 'application/javascript'});
		var worker = new Worker(URL.createObjectURL(blob));
		worker.onerror = reject;
		worker.onmessage = (d)=>{
			resolve(...d.data);
			worker.terminate();
		};
		worker.postMessage(args);
	});
}

new Thread("this is a message", 2, function(message, delaySeconds, exit){

	setTimeout(()=>{
		exit(message.split('').reverse().join(''));
	}, delaySeconds * 1000);

}).then(data=>{
	console.log(data);
}).catch(err=>{
	console.log('error: ', err);
});

// Can be used with or without "new"
Thread(function(exit){

	console.log("logging from thread");
	setTimeout(exit, 1000);

}).then(data=>{
	console.log('done');
}).catch(err=>{
	console.log('error: ', err);
});