Fix issue #1008

snippets/deepClone.md

@@ -11,6 +11,11 @@ Use `Object.keys()` and `Array.prototype.forEach()` to determine which key-value
 
 ```js
 const deepClone = obj => {
+  let type = typeof obj;
+  let isAssignable = type === "function" || type === "object" && !!obj;
+  if (!isAssignable) {
+    return obj;
+  }
   let clone = Object.assign({}, obj);
   Object.keys(clone).forEach(
     key => (clone[key] = typeof obj[key] === 'object' ? deepClone(obj[key]) : obj[key])