Calculate the square root using Newton's method

sqrt.js

function sqrt(n) {
    var xn, d, ld;
    var c = 0; //counter
    var done = false; 
    var delta = 1e-17;
    xn = n/2;
    var safety = 1000;
    do {
        //break if we're not converging
        if(c > safety)
            throw new Error('Unable to calculate square root for '+n);
        xn = (xn+(n/xn))/2;
        //get the difference from the true square
        d = n - (xn*xn);
        //if the square of the calculated number is close enough to the number
        //we're getting the square root or the last delta was the same as the new delta
        //then we're done
        if(Math.abs(d) < delta || ld === d)
            done = true;
        //store the calculated delta
        ld = d; 
        c++; //increase the counter
    }
    while(!done)
    
    return xn;
}