Bump to v4.0.0.

internal/mapHas.js

@@ -1,20 +1,23 @@
-/** Used for native method references. */
-var objectProto = Object.prototype;
-
-/** Used to check objects for own properties. */
-var hasOwnProperty = objectProto.hasOwnProperty;
+import Map from './Map';
+import assocHas from './assocHas';
+import hashHas from './hashHas';
+import isKeyable from './isKeyable';
 
 /**
- * Checks if a cached value for `key` exists.
+ * Checks if a map value for `key` exists.
  *
  * @private
  * @name has
- * @memberOf _.memoize.Cache
+ * @memberOf MapCache
  * @param {string} key The key of the entry to check.
  * @returns {boolean} Returns `true` if an entry for `key` exists, else `false`.
  */
 function mapHas(key) {
-  return key != '__proto__' && hasOwnProperty.call(this.__data__, key);
+  var data = this.__data__;
+  if (isKeyable(key)) {
+    return hashHas(typeof key == 'string' ? data.string : data.hash, key);
+  }
+  return Map ? data.map.has(key) : assocHas(data.map, key);
 }
 
 export default mapHas;