WebAssembly

The same index runs in the browser. With the wasm feature, haystackfm exposes a wasm-bindgen JS/TS API and uses the browser’s WebGPU for GPU construction and queries.

Building the package

cargo add haystackfm --features wasm
wasm-pack build --target web --features wasm

This produces a pkg/ directory containing haystackfm.js, haystackfm_bg.wasm, and .d.ts type definitions.

JS/TS API

import init, { FmIndexBuilder, FmIndexHandle } from "./pkg/haystackfm.js";

await init();

const builder = new FmIndexBuilder(/*sa_sample_rate=*/32);
builder.add_fasta(`>seq1\nACGTACGT\n>seq2\nTGCATGCA`);

const handle = await builder.build_gpu();    // or builder.build_cpu()

console.log(handle.count("ACGT"));           // number of occurrences
console.log(handle.locate("ACGT"));          // Array of [seqId, offset] pairs

// seqId is the sequence's 0-based build order, not its FASTA header.
console.log(handle.seq_header(0));           // "seq1"  — id -> header, O(1)
console.log(handle.seq_id("seq1"));          // 0       — header -> id, O(1)
console.log(handle.seq_headers());           // ["seq1", "seq2"] — indexed by seqId

console.log(handle.text_len());              // total text length
console.log(handle.num_sequences());         // number of indexed sequences

const bytes = handle.to_bytes();             // Uint8Array — serialize
const restored = FmIndexHandle.from_bytes(bytes);

Requirements

GPU builds and queries require a browser with WebGPU. CPU builds (build_cpu) work anywhere WASM runs. See Browser Support, and try the live demo to see it end-to-end.