Add src/index.js

src/index.js

@@ -0,0 +1,30 @@
+function slow(x) {
+  // there can be a heavy CPU-intensive job here
+  console.info(`Called with ${x}`);
+  return x;
+}
+
+function cachingDecorator(func) {
+  let cache = new Map();
+
+  return function(x) {
+    if (cache.has(x)) {    // if there's such key in cache
+      console.info("Cache hit!");
+      return cache.get(x); // read the result from it
+    }
+
+    let result = func(x);  // otherwise call func
+
+    console.info("Cache miss!");
+    cache.set(x, result);  // and cache (remember) the result
+    return result;
+  };
+}
+
+slow = cachingDecorator(slow);
+
+console.info( slow(1) ); // slow(1) is cached and the result returned
+console.info( "Again: " + slow(1) ); // slow(1) result returned from cache
+
+console.info( slow(2) ); // slow(2) is cached and the result returned
+console.info( "Again: " + slow(2) );