feature/cache: Add initial cache function

Author: Intellicode

src/cache.js

@@ -0,0 +1,20 @@
+const hash = require('object-hash');
+
+function cache(func) {
+  return (root, args, context) => {
+    if (!context.resolverCache) {
+      throw new Error('Missing resolverCache property on the Graphql context.');
+    }
+
+    const key = `${hash(root)}:${hash(args)}`;
+    return (
+      context.resolverCache
+        .get(key)
+        .then(result => (result ? result : func(root, args, context)))
+        // Error
+        .catch(() => func(root, args, context))
+    );
+  };
+}
+
+module.exports = cache;