Adding data to NaN values

example.js

console.log(examineNaN(NaN));
// > { isNaN: true, sign: 0, signaling: false, payload: 0 }

const nan = createNaN(false, false, 5000);
console.log(isNaN(nan));
// > true
console.log(examineNaN(nan));
// > { isNaN: true, sign: 0, signaling: false, payload: 5000 }

const nan2 = createNaN(false, false, [1, 2, 3, 4, 5, 6]);
console.log(isNaN(nan2));
// > true
console.log(examineNaN(nan2));
// > { isNaN: true, sign: 0, signaling: false, payload: Uint8Array [ 1, 2, 3, 4, 5, 6 ] }

console.log(examineNaN(nan + 3).payload === examineNaN(nan).payload);
// > true

nan_utils.js

/**
 * @param {boolean} sign false is positive, true is negative
 * @param {boolean} signaling Whether or not this is a signaling NaN
 * @param {number | number[] | Uint8Array} payload A single 32-bit integer or an array of up to 6 bytes.
 */
function createNaN(sign, signaling, payload) {
    const buf = new ArrayBuffer(8);
    const view = new DataView(buf);

    const isByteArray = !('number' === typeof payload);

    if (isByteArray) {
        const byteCount = Math.min(6, payload.length);

        for (let i = 0; i < byteCount; i++) {
            view.setUint8(i + 2, payload[i]);
        }
    } else {
        view.setUint32(4, parseInt(payload), false);
    }

    view.setUint8(0, (sign << 7) | 0b01111111);
    view.setUint8(1, 0b11110100 | ((!signaling) << 3) | isByteArray);

    return view.getFloat64(0);
}

/**
 * @param {number} value 
 */
function examineNaN(value) {
    const buf = new ArrayBuffer(8);
    const view = new DataView(buf);

    view.setFloat64(0, value);

    const ui8_0 = view.getUint8(0);
    const ui8_1 = view.getUint8(1);

    const signValue = (ui8_0 & 0b10000000) >> 7;
    const signalingValue = ui8_1 & 0b00001000;
    const exponentValue = ((ui8_0 & 0b011111111) << 4) | ((ui8_1 & 0b11110000) >> 4);

    view.setUint8(0, 0);
    view.setUint8(1, ui8_1 & 0b00001111);

    const significandValue = view.getFloat64(0);
    const isNaNValue = !!significandValue && exponentValue === 2047;
    const isByteArray = (ui8_1 & 0b00000001);

    return {
        isNaN: isNaNValue,
        sign: signValue,
        signaling: isNaNValue ? !signalingValue : undefined,
        payload: isNaNValue ? (isByteArray ? new Uint8Array(buf, 2, 6) : view.getUint32(4, false)) : undefined
    };
}