id is not required when creating a document. If it's not specified, ES will generate a unique ID for the document.

elasticsearch/elasticsearch-tests.ts

@@ -32,6 +32,11 @@ client.indices.delete({
 }, function (error) {
 });
 
+client.create({
+  index: 'index',
+  type: 'type'
+});
+
 client.create({
   id: '123',
   index: 'index',

elasticsearch/index.d.ts

@@ -195,7 +195,7 @@ declare module Elasticsearch {
         version?: number;
         versionType?: VersionType;
         pipeline?: string;
-        id: string;
+        id?: string;
         index: string;
         type: string;
     }