JavaScript big integer square root

This concerns the new JavaScript BigInt type, as supported in Chrome and Node v10.4

Both the following lines throw an error:

Math.sqrt(9n)
Math.sqrt(BigInt(9))

Error is:

Cannot convert a BigInt value to a number

How do I get the square root of a BigInt in JavaScript? TIA

From here: https://golb.hplar.ch/2018/09/javascript-bigint.html

function sqrt(value) {
    if (value < 0n) {
        throw 'square root of negative numbers is not supported'
    }

    if (value < 2n) {
        return value;
    }

    function newtonIteration(n, x0) {
        const x1 = ((n / x0) + x0) >> 1n;
        if (x0 === x1 || x0 === (x1 - 1n)) {
            return x0;
        }
        return newtonIteration(n, x1);
    }

    return newtonIteration(value, 1n);
}

sqrt(BigInt(9))