How to use the snarkjs.bn128 function in snarkjs

const genPrivKey: PrivKey = () => {

    // Check whether we are using the correct value for SNARK_FIELD_SIZE
    assert(SNARK_FIELD_SIZE.eq(snarkjs.bn128.r))

    // Prevent modulo bias
    const min = (
        (snarkjs.bigInt(2).pow(snarkjs.bigInt(256))) - SNARK_FIELD_SIZE
    ) % SNARK_FIELD_SIZE

    let rand: SnarkBigInt

    while (true) {
        rand = snarkjs.bigInt('0x' + crypto.randomBytes(32).toString('hex'))

        if (rand >= min) {
            break
        }
    }