opencc-fmmseg-wasm

OpenCC FMM segmentation WebAssembly bindings for browsers and JavaScript runtimes.

This package provides high-quality Simplified Chinese ↔ Traditional Chinese conversion powered by the Rust opencc-fmmseg engine.

Features:

• OpenCC-compatible conversion configs
• Pure WebAssembly (no native binaries)
• Browser-friendly
• TypeScript-friendly APIs
• Fast Rust backend
• FMM-based phrase segmentation
• Traditional Chinese regional variants
• Japanese Shinjitai conversion support
• Chinese script detection (zho_check)
• In-memory Office / EPUB document conversion
• Zero-dependency Node.js CLI

Installation

npm install @laisuk/opencc-fmmseg-wasm

Quick Start

import init, {
    OpenccWasm,
    DetofuLevelWasm
} from "@laisuk/opencc-fmmseg-wasm";

await init();

const cc = new OpenccWasm("s2t");

console.log(cc.convert("汉字", false));
// 漢字

console.log(cc.convertDetofu("儼驂騑於上路", false, DetofuLevelWasm.ExtB));
// 俨骖騑于上路

Using Config Enums

import init, {
    OpenccWasm,
    OpenccConfigWasm
} from "@laisuk/opencc-fmmseg-wasm";

await init();

const cc = OpenccWasm.newWithEnum(
    OpenccConfigWasm.S2t
);

console.log(cc.convert("汉字", false));
// 漢字

Supported Configs

| Config | Description | |---------|----------------------------------------------------| | s2t | Simplified Chinese → Traditional Chinese | | s2tw | Simplified Chinese → Taiwan Traditional | | s2twp | Simplified Chinese → Taiwan Traditional (phrases) | | s2hk | Simplified Chinese → Hong Kong Traditional | | t2s | Traditional Chinese → Simplified Chinese | | t2tw | Traditional Chinese → Taiwan Traditional | | t2twp | Traditional Chinese → Taiwan Traditional (phrases) | | t2hk | Traditional Chinese → Hong Kong Traditional | | tw2s | Taiwan Traditional → Simplified Chinese | | tw2sp | Taiwan Traditional → Simplified Chinese (phrases) | | tw2t | Taiwan Traditional → Traditional Chinese | | tw2tp | Taiwan Traditional → Traditional Chinese (phrases) | | hk2s | Hong Kong Traditional → Simplified Chinese | | hk2t | Hong Kong Traditional → Traditional Chinese | | jp2t | Japanese Shinjitai → Traditional Chinese | | t2jp | Traditional Chinese → Japanese Shinjitai |

API

Constructor

const cc = new OpenccWasm("s2t");

Parameters:

• config (optional): OpenCC config string
• default: "s2t"

Example:

const cc = new OpenccWasm("t2s");

convert

cc.convert(text, punctuation)

Parameters:

• text: input string
• punctuation: whether to convert punctuation variants

Returns:

• converted string

Example:

cc.convert("汉字", false);

detofu

Replace tofu-risk rare CJK extension characters with display-compatible fallbacks.

cc.detofu(text, level)

Parameters:

• text: input string
• level: DetofuLevelWasm threshold for the CJK extension ranges to replace

Returns:

• detofu-safe string

Supported levels:

| Enum | CLI value | |------------------------|-----------| | DetofuLevelWasm.ExtB | ext-b | | DetofuLevelWasm.ExtC | ext-c | | DetofuLevelWasm.ExtD | ext-d | | DetofuLevelWasm.ExtE | ext-e | | DetofuLevelWasm.ExtF | ext-f | | DetofuLevelWasm.ExtG | ext-g | | DetofuLevelWasm.ExtH | ext-h | | DetofuLevelWasm.ExtI | ext-i |

Example:

import init, {
    OpenccWasm,
    DetofuLevelWasm
} from "@laisuk/opencc-fmmseg-wasm";

await init();

const cc = new OpenccWasm("t2s");
const converted = cc.convert("儼驂騑於上路", false);

console.log(converted);
// 俨骖𬴂于上路

console.log(cc.detofu(converted, DetofuLevelWasm.ExtB));
// 俨骖騑于上路

convertDetofu

Convert text and apply detofu in one call.

cc.convertDetofu(text, punctuation, level)

Parameters:

• text: input string
• punctuation: whether to convert punctuation variants
• level: DetofuLevelWasm threshold for the CJK extension ranges to replace

Returns:

• converted detofu-safe string

Example:

cc.convertDetofu("儼驂騑於上路", false, DetofuLevelWasm.ExtB);
// 俨骖騑于上路

setConfig

cc.setConfig("t2s");

Returns:

• true if valid
• false if invalid

getConfig

cc.getConfig();

Returns current config string.

isValidConfig

OpenccWasm.isValidConfig("s2t");

getSupportedConfigs

OpenccWasm.getSupportedConfigs();

Returns all supported config strings.

zhoCheck

Detect Chinese script type.

cc.zhoCheck(text);

Returns:

| Value | Meaning | |-------|---------------------| | 0 | Unknown / mixed | | 1 | Traditional Chinese | | 2 | Simplified Chinese |

Office / EPUB Conversion

Office and EPUB conversion runs fully locally in the browser or Node.js. Files are passed in and returned as bytes; nothing is uploaded to a backend server.

This is useful for converting text inside:

docx, xlsx, pptx, odt, ods, odp, epub

File size is limited by available browser or Node.js memory, but there is no upload or server-side limit. Font preservation is supported with the keepFont option.

convert_office_bytes(inputBytes, format, config, punctuation, keepFont)

Parameters:

• inputBytes: Uint8Array document bytes
• format: docx, xlsx, pptx, odt, ods, odp, or epub
• config: OpenCC config string, such as "s2t"
• punctuation: whether to convert punctuation variants
• keepFont: whether to preserve font declarations where supported

Returns:

• converted output bytes

Browser Office Example

import init, {convert_office_bytes} from "@laisuk/opencc-fmmseg-wasm";

await init();

const file = document.querySelector("input[type=file]").files[0];
const inputBytes = new Uint8Array(await file.arrayBuffer());

const outputBytes = convert_office_bytes(
    inputBytes,
    "docx",
    "s2t",
    true,
    true
);

const blob = new Blob([outputBytes], {
    type: "application/vnd.openxmlformats-officedocument.wordprocessingml.document"
});

const a = document.createElement("a");
a.href = URL.createObjectURL(blob);
a.download = "converted.docx";
a.click();
URL.revokeObjectURL(a.href);

Node.js Office Example

import fs from "fs";
import init, {convert_office_bytes} from "@laisuk/opencc-fmmseg-wasm";

await init();

const inputBytes = fs.readFileSync("input.docx");

const outputBytes = convert_office_bytes(
    inputBytes,
    "docx",
    "s2t",
    true,
    true
);

fs.writeFileSync("output.docx", outputBytes);

Browser Example

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>OpenCC WASM Demo</title>
</head>
<body>

<script type="module">
    import init, {
        OpenccWasm
    } from "./pkg/opencc_fmmseg_wasm.js";

    await init();

    const cc = new OpenccWasm("s2t");

    console.log(
            cc.convert("汉字", false)
    );
</script>

</body>
</html>

Node.js CLI

The package includes a zero-dependency Node.js CLI:

opencc-fmmseg convert -i input.txt -o output.txt -c s2t -p
opencc-fmmseg convert -i input.txt -o output.txt -c t2s -p --detofu all

opencc-fmmseg office -i input.docx -o output.docx -c s2t -p --keep-font

Text Conversion Options

-i, --input <file>          Input text file
-o, --output <file>         Output text file
-c, --config <conversion>   Conversion config
-p, --punct                 Enable punctuation conversion
--detofu [level]            Replace tofu-risk rare CJK extension chars after conversion
                              level: all | ext-b | ext-c | ext-d | ext-e | ext-f | ext-g | ext-h | ext-i
                              default when omitted value: all
--in-enc <encoding>         Input encoding
--out-enc <encoding>        Output encoding

Office / EPUB Options

-i, --input <file>          Input Office / EPUB file
-o, --output <file>         Output file
-c, --config <conversion>   Conversion config
-p, --punct                 Enable punctuation conversion
--format <format>           docx | xlsx | pptx | odt | ods | odp | epub
--auto-ext                  Append extension to output if missing
--keep-font                 Preserve font-family information
--no-keep-font              Do not preserve font-family information

For office, the format is inferred from the input file extension when --format is omitted.

If -o, --output is omitted, office writes:

<input-name>_converted.<ext>

TypeScript Support

The package includes generated TypeScript definitions from wasm-bindgen.

The WASM-facing enum is exported as OpenccConfigWasm, alongside OpenccWasm.

Performance Notes

• WebAssembly build disables Rayon parallelism by default.
• Dictionaries are embedded into the WASM binary.
• Browser caching significantly improves subsequent loads.

Related Projects

• Rust backend: https://github.com/laisuk/opencc-fmmseg
• C API: https://github.com/laisuk/opencc-fmmseg/tree/master/capi/opencc-fmmseg-capi
• .NET: https://github.com/laisuk/OpenccNet
• Python: https://github.com/laisuk/opencc_purepy

License

MIT