num min(num a, num b)

Returns the lesser of two numbers.

Returns NaN if either argument is NaN. The lesser of -0.0 and 0.0 is -0.0. If the arguments are otherwise equal (including int and doubles with the same mathematical value) then it is unspecified which of the two arguments is returned.

Source 

num min(num a, num b) {
  // These partially redundant type checks improve code quality for dart2js.
  // Most of the improvement is at call sites from the inferred non-null num
  // return type.
  if (a is! num) throw new ArgumentError(a);
  if (b is! num) throw new ArgumentError(b);

  if (a > b) return b;
  if (a < b) return a;
  if (b is double) {
    // Special case for NaN and -0.0. If one argument is NaN return NaN.
    // [min] must also distinguish between -0.0 and 0.0.
    if (a is double) {
      if (a == 0.0) {
        // a is either 0.0 or -0.0. b is either 0.0, -0.0 or NaN.
        // The following returns -0.0 if either a or b is -0.0, and it
        // returns NaN if b is NaN.
        return (a + b) * a * b;
      }
    }
    // Check for NaN and b == -0.0.
    if (a == 0 && b.isNegative || b.isNaN) return b;
    return a;
  }
  return a;
}