readstat-wasm

WebAssembly build of the readstat library for parsing SAS .sas7bdat files in JavaScript. Reads metadata and converts row data to CSV, NDJSON, Parquet, or Feather (Arrow IPC) entirely in memory — no server or native dependencies required at runtime.

Package contents

The pkg/ directory contains everything needed to use the library from JavaScript:

File	Description
`readstat_wasm.wasm`	Pre-built WASM binary (Emscripten target)
`readstat_wasm.js`	JS wrapper handling module loading, memory management, and type conversion

JS API

All functions accept a Uint8Array of raw .sas7bdat file bytes.

import { init, read_metadata, read_metadata_fast, read_data, read_data_ndjson, read_data_parquet, read_data_feather } from "readstat-wasm";

// Must be called once before using any other function
await init();

const bytes = new Uint8Array(/* .sas7bdat file contents */);

// Metadata (returns JSON string)
const metadataJson = read_metadata(bytes);
const metadataJsonFast = read_metadata_fast(bytes); // skips full row count

// Data as text (returns string)
const csv = read_data(bytes);       // CSV with header row
const ndjson = read_data_ndjson(bytes); // newline-delimited JSON

// Data as binary (returns Uint8Array)
const parquet = read_data_parquet(bytes);  // Parquet bytes
const feather = read_data_feather(bytes);  // Feather (Arrow IPC) bytes

Functions

Function	Returns	Description
`init()`	`Promise<void>`	Load and initialize the WASM module
`read_metadata(bytes)`	`string`	File and variable metadata as JSON
`read_metadata_fast(bytes)`	`string`	Same as above but skips full row count for speed
`read_data(bytes)`	`string`	All row data as CSV (with header)
`read_data_ndjson(bytes)`	`string`	All row data as newline-delimited JSON
`read_data_parquet(bytes)`	`Uint8Array`	All row data as Parquet bytes
`read_data_feather(bytes)`	`Uint8Array`	All row data as Feather (Arrow IPC) bytes

How it works

The crate compiles the ReadStat C library and the Rust readstat parsing library to WebAssembly using the wasm32-unknown-emscripten target. Emscripten is required because the underlying C code needs a C standard library (libc, iconv).

The data functions perform a two-pass parse over the byte buffer: first to extract metadata (schema, row count), then to read row values into an Arrow RecordBatch, which is serialized to CSV, NDJSON, Parquet, or Feather in memory.

C ABI exports

The WASM module exposes these C-compatible functions (used internally by the JS wrapper):

Export	Signature	Purpose
`read_metadata`	`(ptr, len) -> *char`	Parse metadata as JSON
`read_metadata_fast`	`(ptr, len) -> *char`	Same, skipping full row count
`read_data`	`(ptr, len) -> *char`	Parse data, return as CSV
`read_data_ndjson`	`(ptr, len) -> *char`	Parse data, return as NDJSON
`read_data_parquet`	`(ptr, len, out_len) -> *u8`	Parse data, return as Parquet bytes
`read_data_feather`	`(ptr, len, out_len) -> *u8`	Parse data, return as Feather bytes
`free_string`	`(ptr)`	Free a string returned by the above
`free_binary`	`(ptr, len)`	Free a binary buffer returned by parquet/feather

Building from source

Requires Rust, Emscripten SDK, and libclang.

# Activate Emscripten
source /path/to/emsdk/emsdk_env.sh

# Add the target (first time only)
rustup target add wasm32-unknown-emscripten

# Initialize submodules (first time only, from repo root)
git submodule update --init --recursive

# Build
cargo build --target wasm32-unknown-emscripten --release

# Copy binary to pkg/
cp target/wasm32-unknown-emscripten/release/readstat_wasm.wasm pkg/

See the bun-demo for a working example.

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