det.js

function determinant(m) {
  var l = m.length - 1;
  if(l === 0) {
    return m[0][0];
  } else {
    if(l === 1) {
      return m[0][0]*m[l][l]-m[0][l]*m[l][0];
    } else {
      return m.reduce(function (p, c, i, a) {
        var sign = i % 2 === 0 ? 1 : -1;
        var minor = a.slice(0)
        minor.splice(0,1);
        minor = minor.map(function(val) {
          val = val.slice(0);
           val.splice(i,1);
          return val;
        });
        return p + (sign * m[0][i] * determinant(minor));
      }, 0);
    }
  }
};