flatc-wasm

library26.1.32jsnpmunverified

FlatBuffers compiler (flatc) compiled to WebAssembly, enabling schema management, JSON/binary conversion, and code generation in Node.js (18+) and modern browsers without native dependencies. Current stable version 26.1.32, released February 2025. Key differentiators: self-contained with inlined WASM binaries, zero native deps, supports 13 code generation languages (C++, TypeScript, Go, Rust, Python, Java, etc.), per-field AES-256-CTR encryption, streaming APIs for large data, JSON Schema import/export, and embedded language runtimes. Licensed under Apache 2.0. Maintained by DigitalArsenal on GitHub.

serialization data devops

npm install flatc-wasm

github ↗package ↗homepage ↗

INSTALL

IMPORT

SIG · FLATC-WASM

flatc-wasm

serializationjavascriptv26.1.32

harness data pending

Install & Compatibility

Where this runs

No compatibility data collected yet for this library.

Code

Verified usage

Verified import paths — ran on the pinned version, not inferred.

FlatcRunner

✓ import { FlatcRunner } from 'flatc-wasm'

✗ const FlatcRunner = require('flatc-wasm').FlatcRunner

ES module import; also works with dynamic import()

createFlatcModule

✓ import { createFlatcModule } from 'flatc-wasm'

✗ const createFlatcModule = require('flatc-wasm')

Low-level module factory for manual WASM initialization

AlignedType

✓ import { AlignedType } from 'flatc-wasm'

✗ import { AlignedTypes } from 'flatc-wasm'

Enum used for aligned binary format; type import also available: import type { AlignedType }

Demonstrates loading a FlatBuffers schema, converting between JSON and binary, and generating TypeScript code using FlatcRunner.

import { FlatcRunner } from 'flatc-wasm'; import { readFileSync, writeFileSync } from 'fs'; async function main() { // Create runner instance const runner = await FlatcRunner.create(); // Load a FlatBuffers schema const schema = readFileSync('monster.fbs', 'utf8'); await runner.addSchema('monster', schema); // Convert JSON to FlatBuffer binary const jsonData = JSON.stringify({ name: 'Orc', hp: 300 }); const binary = await runner.jsonToBinary('monster', jsonData, 'MyGame.Sample.Monster'); writeFileSync('monster.bin', Buffer.from(binary)); // Convert binary back to JSON (auto-detects schema) const binaryBuf = readFileSync('monster.bin'); const jsonOut = await runner.binaryToJson('monster', new Uint8Array(binaryBuf)); console.log(jsonOut); // Generate TypeScript code const tsCode = await runner.generateCode('monster', 'typescript'); writeFileSync('monster_generated.ts', tsCode); } main().catch(console.error);

Debug

Known issues

breakingWASM module initialization changed from synchronous to async in v26.0.0. FlatcRunner.create() must be awaited.

fix

Use await FlatcRunner.create() instead of new FlatcRunner().

affects: >=26.0.0

deprecatedThe low-level API 'createFlatcModule' is deprecated in favor of 'FlatcRunner' since v25.12.0.

fix

Migrate to FlatcRunner API for easier usage and better error handling.

affects: >=25.12.0

gotchaBinary output from jsonToBinary is an ArrayBuffer, not a Buffer. Use Buffer.from() before writing to file.

fix

const buffer = Buffer.from(await runner.jsonToBinary(...));

affects: >=0.0.0

breakingNode.js minimum version raised to 18.0.0 in v25.0.0. Older versions are not supported.

fix

Upgrade Node.js to 18.0.0 or later.

affects: >=25.0.0

gotchaSchema names are case-sensitive and must match the schema file name (without .fbs). Adding a schema with the wrong name will fail silently.

fix

Ensure schema name matches the file stem, e.g., 'monster' for 'monster.fbs'.

affects: >=0.0.0

Errors

Common errors & fixes

Error: WebAssembly.instantiate(): expected magic word 00 61 73 6d

The WASM binary is corrupted or not fully loaded due to network issues in browser or incorrect bundler configuration.

fix

Ensure the WASM binary is served with the correct MIME type 'application/wasm' and loaded via fetch or import. In webpack, add a rule to load .wasm files as WebAssemblyModule.

TypeError: Cannot read properties of undefined (reading 'addSchema')

FlatcRunner.create() not awaited; runner object is undefined.

fix

Use const runner = await FlatcRunner.create();

Error: Schema 'monster' not found

Schema was not added before calling conversion or code generation functions.

fix

Call await runner.addSchema('monster', schemaContent) first.

RangeError: offset is out of bounds

ArrayBuffer passed to binaryToJson is too small or the binary format is malformed.

fix

Verify that the binary was generated by flatc or by jsonToBinary with the correct schema and root type.

Upgrade

Version history

26.1.32latest on npm

Audit

Dependencies

hd-wallet-wasmoptionalOptional dependency for HD key derivation used in encryption features

Agent activity

4 hits · last 30 days

node

Resources

githubhttps://github.com/DigitalArsenal/flatbuffers ↗

packagehttps://www.npmjs.com/package/flatc-wasm ↗

homepagehttps://flatbuffers.dev/ ↗