---
title: Configuration
sidebar_position: 4
id: configuration
license: |
  Licensed to the Apache Software Foundation (ASF) under one or more
  contributor license agreements.  See the NOTICE file distributed with
  this work for additional information regarding copyright ownership.
  The ASF licenses this file to You under the Apache License, Version 2.0
  (the "License"); you may not use this file except in compliance with
  the License.  You may obtain a copy of the License at

     http://www.apache.org/licenses/LICENSE-2.0

  Unless required by applicable law or agreed to in writing, software
  distributed under the License is distributed on an "AS IS" BASIS,
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing permissions and
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---

Fory JavaScript is an xlang-only implementation. `new Fory()` writes xlang payloads and uses compatible
schema evolution by default. There is no native-mode switch in the JavaScript API.

## Basic Configuration

```ts
import Fory from "@apache-fory/core";

const fory = new Fory();
```

Create one `Fory` instance per application area and reuse it. Registration generates and caches
serializer code for each schema.

## Constructor Options

```ts
import Fory from "@apache-fory/core";
import hps from "@apache-fory/hps";

const fory = new Fory({
  ref: true,
  compatible: true,
  maxDepth: 100,
  maxGraphMemoryBytes: 128 * 1024 * 1024,
  maxUnbackedContainerItems: 8192,
  maxTypeFields: 512,
  maxTypeMetaBytes: 4096,
  maxSchemaVersionsPerType: 10,
  maxAverageSchemaVersionsPerType: 3,
  hps,
});
```

| Option                            | Default   | Description                                                                           |
| --------------------------------- | --------- | ------------------------------------------------------------------------------------- |
| `ref`                             | `false`   | Enable reference tracking for shared or circular object graphs                        |
| `compatible`                      | `true`    | Allow field additions/removals without breaking existing messages                     |
| `maxDepth`                        | `50`      | Maximum nesting depth. Must be `>= 2`. Increase for deeply nested structures          |
| `maxGraphMemoryBytes`             | `128 MiB` | Approximate graph-memory gate accepted during one root deserialization                |
| `maxUnbackedContainerItems`       | `8192`    | Unbacked collection elements and map entries allowed during one root deserialization  |
| `maxTypeFields`                   | `512`     | Maximum fields accepted in one received remote struct metadata body                   |
| `maxTypeMetaBytes`                | `4096`    | Maximum encoded body bytes accepted for one received TypeMeta body                    |
| `maxSchemaVersionsPerType`        | `10`      | Maximum accepted remote metadata versions for one logical type                        |
| `maxAverageSchemaVersionsPerType` | `3`       | Average accepted remote metadata versions across accepted remote types                |
| `useSliceString`                  | `false`   | Optional string-reading optimization for Node.js. Leave at default unless benchmarked |
| `hps`                             | unset     | Optional fast string helper from `@apache-fory/hps` (Node.js 20+)                     |
| `hooks.afterCodeGenerated`        | unset     | Callback to inspect the generated serializer code, useful for debugging               |

## Reference Tracking

Global reference tracking must be enabled before field-level reference metadata can take effect:

```ts
const fory = new Fory({ ref: true });
```

Then mark reference-tracked fields in the schema, for example with
`Type.struct("example.node").setTrackingRef(true)`. See [References](references.md) and
[Schema Metadata](schema-metadata.md).

## Compatible Schema Evolution

Compatible mode is the default. To use faster serialization and smaller size:

```ts
const fory = new Fory({ compatible: false });
```

Use compatible mode for rolling upgrades, independently deployed services, and
cross-language payloads. Use `compatible: false` only when every reader and
writer always uses the same struct schema and you want faster serialization and
smaller size. For individual structs, `evolving: false` applies the same opt-out
to that struct. For cross-language payloads, set `compatible: false` only after
verifying that every language uses the same schema, or when native types are
generated from Fory schema IDL. See [Schema Evolution](schema-evolution.md).

## Graph Memory Budget

`maxGraphMemoryBytes` sets an approximate graph-memory gate for one root deserialization. The
estimate mainly covers materialized arrays, sets, maps, structs, and objects. It skips leaf values
such as strings, binary data, primitive scalars, and dense primitive arrays, so actual JavaScript
heap use can be higher than this value. Leaf values remain protected by byte-availability checks: if
the unread input does not contain enough bytes, Fory will not read or create that leaf value. The
default is a fixed `128 MiB` and is not derived from input size.

Use a positive byte value to set an explicit lower or higher limit:

```ts
const fory = new Fory({
  maxGraphMemoryBytes: 32 * 1024 * 1024,
});
```

Explicit non-positive values are rejected when the Fory instance is created.

String, binary, and dedicated dense primitive array payloads keep their normal
byte-size checks and do not consume this graph budget. Raise the limit only for
trusted workloads that legitimately contain very compact object graphs.

## Unbacked Container Work Budget

`maxUnbackedContainerItems` limits collection elements and map entries whose
repeated read bodies do not consume proportional input during one root
deserialization. The default is `8192`; zero is a strict limit. Raise it only
for trusted payloads that intentionally use compact zero-byte codecs.

## Optional HPS String Path

`@apache-fory/hps` provides an optional Node.js string fast path:

```ts
import hps from "@apache-fory/hps";

const fory = new Fory({ hps });
```

Leave this unset unless you run on Node.js 20+ and have benchmarked your workload.

## Security

See [JavaScript/TypeScript Security](security.md) for trust boundaries, safe reader configuration, and verification.

## Related Topics

- [Basic Serialization](basic-serialization.md)
- [Schema Metadata](schema-metadata.md)
- [Schema Evolution](schema-evolution.md)
- [References](references.md)