Initial release!

.gitignore

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+node_modules
+dist
+package-lock.json
+.DS_Store

README.md

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+# jsdom-worker
+
+This is an experimental implementation of the Web Worker API (specifically Dedicated Worker) for JSDOM.
+
+It does not currently do any real threading, rather it implements the `Worker` interface but all work is done in the current thread.  `jsdom-worker` runs wherever JSDOM runs, and does not require Node.
+
+It supports both "inline" _(created via Blob)_ and standard _(loaded via URL)_ workers.
+
+> **Hot Take:** this module likely works in the browser, where it could act as a simple inline worker "poorlyfill".
+
+## Why?
+
+Jest uses a JSDOM environment by default, which means it doesn't support Workers. This means it is impossible to test code that requires both NodeJS functionality _and_ Web Workers.  `jsdom-worker` implements enough of the Worker spec that it is now possible to do so.
+
+## Installation
+
+`npm i jsdom-worker`
+
+## Example
+
+```js
+import 'jsdom-global/register'
+import 'jsdom-worker'
+
+let code = `onmessage = e => postMessage(e.data*2)`
+let worker = new Worker(URL.createObjectURL(new Blob([code])))
+worker.onmessage = console.log
+worker.postMessage(5)  // 10
+```
+
+## Usage with Jest
+
+For single tests, simply add `import 'jsdom-worker'` to your module.
+
+Otherwise, add it via the [setupFiles](https://facebook.github.io/jest/docs/en/configuration.html#setupfiles-array) Jest config option:
+
+```js
+{
+  "setupFiles": [
+    "jsdom-worker"
+  ]
+}
+```
+
+## License
+
+[MIT License](https://oss.ninja/mit/developit)

package.json

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+{
+  "name": "jsdom-worker",
+  "version": "0.1.0",
+  "description": "Experimental Web Worker API implementation for JSDOM.",
+  "main": "dist/jsdom-inline-worker.js",
+  "module": "dist/jsdom-inline-worker.m.js",
+  "scripts": {
+    "prepare": "microbundle --external all",
+    "test": "eslint src test && npm run -s prepare && jest"
+  },
+  "babel": {
+    "presets": [
+      "env"
+    ]
+  },
+  "keywords": [
+    "jsdom",
+    "web worker"
+  ],
+  "eslintConfig": {
+    "extends": "eslint-config-developit"
+  },
+  "author": "Jason Miller <jason@developit.ca> (http://jasonformat.com)",
+  "license": "MIT",
+  "files": [
+    "dist"
+  ],
+  "devDependencies": {
+    "babel-jest": "^22.1.0",
+    "babel-preset-env": "^1.6.1",
+    "eslint": "^4.16.0",
+    "eslint-config-developit": "^1.1.1",
+    "jest": "^22.1.4",
+    "microbundle": "^0.4.3",
+    "node-fetch": "^1.7.3"
+  },
+  "peerDependencies": {
+    "node-fetch": "*"
+  },
+  "dependencies": {
+    "mitt": "^1.1.3",
+    "uuid-v4": "^0.1.0"
+  }
+}

src/index.js

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+import mitt from 'mitt';
+import uuid from 'uuid-v4';
+import fetch, { Response } from 'node-fetch';
+
+if (!global.URL) global.URL = {};
+if (!global.URL.$$objects) {
+	global.URL.$$objects = new Map();
+	global.URL.createObjectURL = blob => {
+		let id = uuid();
+		global.URL.$$objects[id] = blob;
+		return `blob:http://localhost/${id}`;
+	};
+
+	let oldFetch = global.fetch || fetch;
+	global.fetch = function(url, opts) {
+		if (url.match(/^blob:/)) {
+			return new Promise( (resolve, reject) => {
+				let fr = new FileReader();
+				fr.onload = () => {
+					let Res = global.Response || Response;
+					resolve(new Res(fr.result, { status: 200, statusText: 'OK' }));
+				};
+				fr.onerror = () => {
+					reject(fr.error);
+				};
+				let id = url.match(/[^/]+$/)[0];
+				fr.readAsText(global.URL.$$objects[id]);
+			});
+		}
+		return oldFetch.call(this, url, opts);
+	};
+}
+
+if (!global.document) {
+	global.document = {};
+}
+
+function Event(type) { this.type = type; }
+if (!global.document.createEvent) {
+	global.document.createEvent = function(type) {
+		let Ctor = global[type] || Event;
+		return new Ctor(type);
+	};
+}
+
+
+global.Worker = function Worker(url) {
+	let messageQueue = [],
+		inside = mitt(),
+		outside = mitt(),
+		scope = {
+			onmessage: null,
+			dispatchEvent: inside.emit,
+			addEventListener: inside.on,
+			removeEventListener: inside.off,
+			postMessage(data) {
+				outside.emit('message', { data });
+			},
+			fetch: global.fetch
+		},
+		getScopeVar;
+	inside.on('message', e => { let f = getScopeVar('onmessage'); if (f) f.call(scope, e); });
+	this.addEventListener = outside.on;
+	this.removeEventListener = outside.off;
+	this.dispatchEvent = outside.emit;
+	outside.on('message', e => { this.onmessage && this.onmessage(e); });
+	this.postMessage = data => {
+		if (messageQueue!=null) messageQueue.push(data);
+		else inside.emit('message', { data });
+	};
+	this.terminate = () => {
+		throw Error('Not Supported');
+	};
+	global.fetch(url)
+		.then( r => r.text() )
+		.then( code => {
+			let vars = 'var self=this,global=self';
+			for (let k in scope) vars += `,${k}=self.${k}`;
+			// eval('(function() {'+vars+'\n'+code+'\n})').call(scope);
+			getScopeVar = eval('(function() {'+vars+'\n'+code+'\nreturn function(__){return eval(__)}})').call(scope);
+			let q = messageQueue;
+			messageQueue = null;
+			q.forEach(this.postMessage);
+		})
+		.catch( e => { outside.emit('error', e); console.error(e); });
+};

test/index.test.js

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+import 'jsdom-worker';
+
+const sleep = t => new Promise( r => { setTimeout(r, t); });
+
+describe('jsdom-worker', () => {
+	it('should work', async () => {
+		let code = `onmessage = e => { postMessage(e.data*2) }`;
+		let worker = new Worker(URL.createObjectURL(new Blob([code])));
+		worker.onmessage = jest.fn();
+		worker.postMessage(5);
+		await sleep(10);
+		expect(worker.onmessage).toHaveBeenCalledWith({ data: 10 });
+	});
+});