multithreading/src/lib/transferable.js

The missing standard library for multithreading in JavaScript (Works in the browser, Node.js, Deno, Bun).

const CANDIDATES = [
    "ArrayBuffer",
    "MessagePort",
    "ReadableStream",
    "WritableStream",
    "TransformStream",
    "OffscreenCanvas",
    "ImageBitmap",
    "VideoFrame",
    "AudioData",
    "RTCDataChannel",
];
// Pre-compute the available constructors once.
// We use a dense array to avoid sparse array lookups.
const CONSTRUCTORS = [];
const G = globalThis;
for (let i = 0; i < CANDIDATES.length; i++) {
    const ctor = G[CANDIDATES[i]];
    if (typeof ctor !== "undefined") {
        CONSTRUCTORS.push(ctor);
    }
}
// Cache length to avoid property lookup in the hot loop
const LEN = CONSTRUCTORS.length;
// Cache ArrayBuffer specifically if it exists (it's index 0 usually)
// This allows a "Fast Path" for the most common transfer type.
const AB = G.ArrayBuffer;
class TransferableInstance {
    static [Symbol.hasInstance](instance) {
        // Fast Fail: Null check
        if (!instance)
            return false;
        // Fast Fail: Primitive check
        // "object" check excludes primitives. Transferables are never functions,
        // and typeof function !== 'object', so this correctly filters functions too.
        if (typeof instance !== "object")
            return false;
        // Fast Path: ArrayBuffer
        // 90% of transferables are ArrayBuffers. Check this O(1) before entering the loop.
        if (AB && instance instanceof AB)
            return true;
        for (let i = 0; i < LEN; i++) {
            if (instance instanceof CONSTRUCTORS[i])
                return true;
        }
        return false;
    }
}
export const Transferable = TransferableInstance;