Bytes array to BigInt in Typescript

byte-array-to-big-int.ts

const MAX_UINT_8 = BigInt(256)
const MAX_UINT_16 = BigInt(65536)
const MAX_UINT_32 = BigInt(4294967296)
const MAX_UINT_64 = BigInt(18446744073709551616)

export const ByteArrayToInt = (value: Uint8Array, isNegative: boolean): BigInt => {
    let n = BigInt(0);
    let MAX = MAX_UINT_8
    switch(value.length){
        case 1:
            MAX = MAX_UINT_8
            break;
        case 2:
            MAX = MAX_UINT_16
            break;
        case 4:
            MAX = MAX_UINT_32
            break;
        case 8:
            MAX = MAX_UINT_64
            break;
    }

    const readBigUInt64LE = (buffer: Buffer, offset = 0) => {
        const first = buffer[offset];
        const last = buffer[offset + 7];
        if (first === undefined || last === undefined) {
          throw new Error('Out of bounds');
        }
      
        const lo = first +
          buffer[++offset] * 2 ** 8 +
          buffer[++offset] * 2 ** 16 +
          buffer[++offset] * 2 ** 24;
      
        const hi = buffer[++offset] +
          buffer[++offset] * 2 ** 8 +
          buffer[++offset] * 2 ** 16 +
          last * 2 ** 24;
      
        return BigInt(lo) + (BigInt(hi) << BigInt(32));
    }

    if (value.length == 8) {
        n = readBigUInt64LE(Buffer.from(value), 0)
    } else {
        switch (value.length){
            case 4:
                n = BigInt(Buffer.from(value).readUInt32LE(0))
                break;
            case 2:
                n = BigInt(Buffer.from(value).readUInt16LE(0))
                break;
            case 1:
                n = BigInt(value[0])
                break;

        }
    }

    if (isNegative) {
        n -= MAX 
    }

    return n
}