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/*=T*/ min/*<T extends num>*/(num/*=T*/ a, num/*=T*/ 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;
}