Run results for: BigInt to BigEndian Bytes

Test name	Executions per second
✓ Direct Constructor	7,495,234 Ops/sec
Direct ParseInt	2,304,316 Ops/sec
DataView	1,995,301 Ops/sec
Loop Constructor	1,943,019 Ops/sec
Loop ParseInt	1,828,028 Ops/sec

Script Preparation code:

function bigIntToBigEndianBytesLoopParseInt(value) {
    const hex = value.toString(16).padStart(16, '0');
    const bytes = new Uint8Array(8);
    for (let i = 0; i < 8; i++) {
        bytes[i] = parseInt(hex.slice(i * 2, i * 2 + 2), 16);
    }
    return bytes;
}

function bigIntToBigEndianBytesLoopConstructor(value) {
    const hex = value.toString(16).padStart(16, '0');
    const bytes = new Uint8Array(8);
    for (let i = 0; i < 8; i++) {
        bytes[i] = Number(hex.slice(i * 2, i * 2 + 2), 16);
    }
    return bytes;
}

function bigIntToBigEndianBytesDataView(value) {
    const buf = new ArrayBuffer(8);
    const view = new DataView(buf);

    view.setBigUint64(0, value);
    return new Uint8Array(buf);
}

function bigIntToUint8ArrayDirectConstructor(value) {
    const result = new Uint8Array(8);
    result[7] = Number(value & 0xffn);
    result[6] = Number((value >> 8n) & 0xffn);
    result[5] = Number((value >> 16n) & 0xffn);
    result[4] = Number((value >> 24n) & 0xffn );
    result[3] = Number((value >> 32n) & 0xffn);
    result[2] = Number((value >> 40n) & 0xffn);
    result[1] = Number((value >> 48n) & 0xffn);
    result[0] = Number((value >> 56n) & 0xffn);
    return result;
}

function bigIntToUint8ArrayDirectParseInt(value) {
    const result = new Uint8Array(8);
    result[7] = parseInt(value & 0xffn);
    result[6] = parseInt((value >> 8n) & 0xffn);
    result[5] = parseInt((value >> 16n) & 0xffn);
    result[4] = parseInt((value >> 24n) & 0xffn );
    result[3] = parseInt((value >> 32n) & 0xffn);
    result[2] = parseInt((value >> 40n) & 0xffn);
    result[1] = parseInt((value >> 48n) & 0xffn);
    result[0] = parseInt((value >> 56n) & 0xffn);
    return result;
}

Tests:

Loop ParseInt
bigIntToBigEndianBytesLoopParseInt(32149814014n)
Loop Constructor
bigIntToBigEndianBytesLoopConstructor(32149814014n)
DataView
bigIntToBigEndianBytesDataView(32149814014n)
Direct Constructor
bigIntToUint8ArrayDirectConstructor(32149814014n)
Direct ParseInt
bigIntToUint8ArrayDirectParseInt(32149814014n)

Run results for: BigInt to BigEndian Bytes

Loop ParseInt

Loop Constructor

DataView

Direct Constructor

Direct ParseInt