Add: worker util

js/worker-util.js

@@ -0,0 +1,101 @@
+/* global importScripts */
+'use strict';
+
+// eslint-disable-next-line no-var
+var workerUtil = (() => {
+  const loadedScripts = new Set();
+  return {createWorker, createAPI, loadScript, cloneError};
+
+  function createWorker({url, lifeTime = 30}) {
+    let worker;
+    let id;
+    let timer;
+    const pendingResponse = new Map();
+
+    return new Proxy({}, {
+      get: (target, prop) =>
+        (...args) => {
+          if (!worker) {
+            init();
+          }
+          return invoke(prop, args);
+        }
+    });
+
+    function init() {
+      id = 0;
+      worker = new Worker(url);
+      worker.onmessage = onMessage;
+    }
+
+    function uninit() {
+      worker.onmessage = null;
+      worker.terminate();
+      worker = null;
+    }
+
+    function onMessage(e) {
+      const message = e.data;
+      pendingResponse.get(message.id)[message.error ? 'reject' : 'resolve'](message.data);
+      pendingResponse.delete(message.id);
+      if (!pendingResponse.size && lifeTime >= 0) {
+        timer = setTimeout(uninit, lifeTime * 1000);
+      }
+    }
+
+    function invoke(action, args) {
+      return new Promise((resolve, reject) => {
+        pendingResponse.set(id, {resolve, reject});
+        clearTimeout(timer);
+        worker.postMessage({
+          id,
+          action,
+          args
+        });
+        id++;
+      });
+    }
+  }
+
+  function createAPI(methods) {
+    self.onmessage = e => {
+      const message = e.data;
+      Promise.resolve()
+        .then(() => methods[message.action](...message.args))
+        .then(result => ({
+          id: message.id,
+          error: false,
+          data: result
+        }))
+        .catch(err => ({
+          id: message.id,
+          error: true,
+          data: cloneError(err)
+        }))
+        .then(data => self.postMessage(data));
+    };
+  }
+
+  function cloneError(err) {
+    return Object.assign({
+      name: err.name,
+      stack: err.stack,
+      message: err.message,
+      lineNumber: err.lineNumber,
+      columnNumber: err.columnNumber,
+      fileName: err.fileName
+    }, err);
+  }
+
+  function loadScript(scripts) {
+    if (!Array.isArray(scripts)) {
+      scripts = [scripts];
+    }
+    const urls = scripts.filter(u => !loadedScripts.has(u));
+    if (!urls.length) {
+      return;
+    }
+    importScripts(...urls);
+    urls.forEach(u => loadedScripts.add(u));
+  }
+})();