Bump to v4.0.0.

internal/assocHas.js

@@ -0,0 +1,15 @@
+import assocIndexOf from './assocIndexOf';
+
+/**
+ * Checks if an associative array value for `key` exists.
+ *
+ * @private
+ * @param {Array} array The array to query.
+ * @param {string} key The key of the entry to check.
+ * @returns {boolean} Returns `true` if an entry for `key` exists, else `false`.
+ */
+function assocHas(array, key) {
+  return assocIndexOf(array, key) > -1;
+}
+
+export default assocHas;