Hypergeometric JS from http://www.math.ucla.edu/~tom/distributions/Hypergeometric.html

hypergeometric.js

//enter with m<nn/2 and n<nn/2

function hyp(x, n, m, nn) {
  var nz, mz;
  // best to have n<m
  if (m < n) {
    nz = m;
    mz = n
  } else {
    nz = n;
    mz = m
  }
  var h=1;
  var s=1;
  var k=0;
  var i=0;
  while (i < x) {
    while (s > 1 && k < nz) {
      h = h * (1 - mz / (nn - k));
      s = s * (1 -mz / (nn - k));
      k = k + 1;
    }
    h = h * (nz - i) * (mz - i) / (i + 1) / (nn - nz - mz + i + 1);
    s = s + h;
    i = i + 1;
  }
  while (k < nz) {
    s = s * (1 - mz / (nn - k));
    k = k + 1;
  }
  return s;
}

function compute(form) {
  var nn = Math.floor(eval(form.pop1.value));
  var m = Math.floor(eval(form.pop2.value));
  var n = Math.floor(eval(form.sample.value));
  var x = Math.floor(eval(form.argument.value));
  var Prob;
  if (n <= 0 || m <= 0 || nn <= 0) {
    alert("Parameters must be positive integers");
    Prob = 0;
  } else if (m > nn || n > nn) {
    alert("m and n must be less than N");
    Prob = 0;
  } else if (x < 0 || x < n + m - nn) {
    Prob = 0;
  } else if (x >= n || x >= m) {
    Prob = 1;
  } else {
    if (2 * m > nn) {
      if (2 * n > nn) {
        Prob = hyp(nn - m - n + x, nn - n, nn - m, nn);
      } else {
        Prob = 1 - hyp(n - x - 1, n, nn - m, nn);
      }
    } else if (2 * n > nn) {
      Prob = 1 - hyp(m - x - 1, m, nn - n, nn);
    } else {
      Prob = hyp(x, n, m, nn)
    }
  }
  Prob = Math.round(Prob * 100000) / 100000;
  form.result.value = Prob;
}