wickra/docs/wiki/Quickstart-WASM.md

Quickstart: WebAssembly

A five-minute tour of the Wickra WebAssembly binding. The same Rust core that powers the Python, Node, and Rust APIs is compiled to WebAssembly with wasm-bindgen, so indicators run entirely client-side — in a browser tab, a bundler build, or Node — with no server round-trips.

Install

The published package is wickra-wasm on npm:

npm install wickra-wasm

The npm package is built for the bundler target, so it works directly with Webpack, Vite, Rollup, and similar toolchains.

Build from source

To build the binding yourself you need wasm-pack and the wasm32-unknown-unknown target:

rustup target add wasm32-unknown-unknown
cargo install wasm-pack

# Browser ES-module build (import directly from a <script type="module">):
wasm-pack build bindings/wasm --target web --release --features panic-hook

# Bundler build (Webpack / Vite / Rollup):
wasm-pack build bindings/wasm --target bundler --release --features panic-hook

wasm-pack writes the generated module, the .wasm binary, and TypeScript definitions into bindings/wasm/pkg/. The panic-hook feature routes Rust panics to console.error for readable stack traces during development.

A first run (browser)

With a --target web build, import the generated module directly:

<script type="module">
  import init, { version, SMA } from "./pkg/wickra_wasm.js";

  await init();                       // load and instantiate the .wasm binary
  console.log("wickra-wasm", version());

  const sma = new SMA(3);
  console.log(sma.batch([2, 4, 6, 8, 10]));
  // -> Float64Array [ NaN, NaN, 4, 6, 8 ]
</script>

init() must be awaited once before any indicator is constructed — it fetches and instantiates the WebAssembly binary. After that the API mirrors the other bindings.

Streaming

import init, { RSI } from "wickra-wasm";

await init();

const rsi = new RSI(14);
for (const price of liveFeed) {
  const value = rsi.update(price);    // number, or null/undefined during warmup
  if (value != null && value > 70) {
    console.log("overbought");
  }
}

Every indicator is an O(1)-per-update state machine: update advances the indicator by exactly one input, so a browser charting app pays no cost for recomputing history on each tick.

Multi-output indicators

Several indicators return a structured object from update (or null during warmup). The full list and their field names:

Indicator	update return shape
MACD	{ macd, signal, histogram }
BollingerBands	{ upper, middle, lower, stddev }
Stochastic	{ k, d }
ADX	{ plusDi, minusDi, adx }
Keltner	{ upper, middle, lower }
Donchian	{ upper, middle, lower }
Aroon	{ up, down }
SuperTrend	{ value, direction }

import init, { MACD } from "wickra-wasm";

await init();

const macd = new MACD(12, 26, 9);
let last = null;
for (let i = 0; i < 40; i++) {
  last = macd.update(100 + i * 0.5);  // null during warmup, else { macd, signal, histogram }
}
console.log(last);

batch returns a flat Float64Array; multi-output indicators interleave their fields per row (e.g. MACD: [macd0, signal0, hist0, macd1, ...]). The exact layout is documented in the generated pkg/wickra_wasm.d.ts.

Since wickra-wasm@0.2.1, every candle-input indicator (ATR, ADX, WilliamsR, CCI, MFI, PSAR, Keltner, Donchian, VWAP, RollingVWAP, AwesomeOscillator, Aroon, Stochastic, OBV, and the rest of the volume / volatility / trailing-stop / price-statistics families) exposes the same streaming API as MACD here — update, batch, reset, isReady and warmupPeriod. Earlier releases only shipped batch for twelve of these classes; browser code no longer needs to replay batch on every tick.

Errors

Unlike the Node binding (whose constructors clamp pathological values), the WASM binding's constructors throw a JavaScript error for invalid parameters:

try {
  new MACD(0, 0, 0);
} catch (e) {
  console.error("invalid MACD parameters:", e);
}

A complete example

examples/wasm/index.html is a self-contained browser demo: it streams a synthetic price series through six indicators and draws a live chart on a <canvas>. Open it after a --target web build:

wasm-pack build bindings/wasm --target web --release --features panic-hook
# then serve the repository root and open examples/wasm/index.html

See also

• Quickstart: Node — the native (non-WASM) Node binding.
• Streaming vs Batch — why update is the primary entry point.
• Indicators Overview — every indicator and its parameters.
• Source: https://github.com/kingchenc/wickra