Add async memoize implementation from Metasync library

tshemsedinov · tshemsedinov · commit 0c9f1aee22ce · 2017-11-21T06:22:47.000+02:00
diff --git a/JavaScript/6-metasync.js b/JavaScript/6-metasync.js
@@ -0,0 +1,58 @@
+'use strict';
+
+const fs = require('fs');
+const util = require('util');
+
+// Production implementation from Metasync library
+// See: https://github.com/metarhia/metasync
+
+const metasync = {};
+
+function Memoized() {
+}
+
+util.inherits(Memoized, Function);
+
+metasync.memoize = (fn) => {
+  const cache = new Map();
+
+  const memoized = function(...args) {
+    const callback = args.pop();
+    const key = args[0];
+    const record = cache.get(key);
+    if (record) {
+      callback(record.err, record.data);
+      return;
+    }
+    fn(...args, (err, data) => {
+      cache.set(key, { err, data });
+      callback(err, data);
+    });
+  };
+
+  const fields = {
+    cache,
+    timeout: 0,
+    limit: 0,
+    size: 0,
+    maxSize: 0
+  };
+
+  Object.setPrototypeOf(memoized, Memoized.prototype);
+  return Object.assign(memoized, fields);
+};
+
+Memoized.prototype.clear = function() {
+  this.cache.clear();
+};
+
+// Usage
+
+fs.readFile = metasync.memoize(fs.readFile);
+
+fs.readFile('6-metasync.js', (err, data) => {
+  console.log('data length: ' + data.length);
+  fs.readFile('6-metasync.js', (err, data) => {
+    console.log('data length: ' + data.length);
+  });
+});
