BigInt to bytes array in TS

int-to-byte-array.ts

const TWO = BigInt(2)
const ONE = BigInt(1)
const ZERO = BigInt(0)
const MINUS = BigInt(-1)

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

const intToByteArray = (val: BigInt, valType: 'int8' | 'int16' | 'int32' | 'int64', isUnsigned: boolean) => {
    const M = {'int8': MAX_UINT_8, 'int16': MAX_UINT_16, 'int32': MAX_UINT_32, 'int64': MAX_UINT_64}[valType]
    const N_BYTE = {'int8': 8, 'int16': 16, 'int32': 32, 'int64': 64}[valType]
    const CURRENT_MIN_INT = (M / TWO) * MINUS
    const CURRENT_MAX_INT = (M / TWO) - ONE

     if (!isUnsigned && (val < CURRENT_MIN_INT || val > CURRENT_MAX_INT)){
        throw new Error("overflow")
    } else if (isUnsigned && (val < ZERO || val > ((CURRENT_MAX_INT * TWO) + ONE))){
        throw new Error("unsigned overflow")
    }

    if (val < ZERO) {
        val = ((CURRENT_MAX_INT+ONE) * TWO) + BigInt(val)
    }

    let binary = val.toString(2);
    const length = N_BYTE - binary.length
    for (var i = 0; i < length; i++){
        binary = `0${binary}`
    }
    
    var ret = new Uint8Array(binary.length / 8)
    i = 0;
    while (i < binary.length){
        ret[(binary.length / 8) - 1 - i] = parseInt(binary.substr(i, 8), 2)
        i += 8
    }
    return ret
}