How to use the big-integer.rand function in big-integer

const getCoprime = (target) => {
  const bits = Math.floor(Math.log2(target))
  while (true) {
    const lowerBound = bigInt(2).pow(bits-1).plus(1)
    const size = bigInt(2).pow(bits).subtract(lowerBound)
    let possible = lowerBound.plus(bigInt.rand(bits)).or(1)
    const result = bigInt(possible)
    if (possible.gt(bigInt(2).pow(1024))) return result
    while(target > 0) {
      [possible, target] = [target, possible.mod(target)]
    }
    if (possible.eq(bigInt(1))) return result
  }
}