The domain and range of the function \( f(x) = 4 \) are:
\[
\text{Domain} = \{ x \mid x \in \mathbb{R} \}, \quad \text{Range} = \{ 4 \}
\]
The answer is boxed as follows:
\[
\boxed{\text{Domain: } \{ x \mid x \in \mathbb{R} \}, \text{ Range: } \{ 4 \}}
\]