from typing import List


def utf8_encode(text: str) -> List[int]:
    """Text as UTF-8 bytes.

    A Python str can hold a lone surrogate (json.loads("\\"\\\\ud800\\"") makes
    one), which str.encode refuses; it becomes U+FFFD here, as TextEncoder
    does in the browser, so the three languages agree.
    """
    if not isinstance(text, str):
        raise TypeError("text must be a string")
    out = []
    for ch in text:
        cp = ord(ch)
        if 0xD800 <= cp <= 0xDFFF:
            cp = 0xFFFD
        if cp < 0x80:
            out.append(cp)
        elif cp < 0x800:
            out.extend((0xC0 | (cp >> 6), 0x80 | (cp & 63)))
        elif cp < 0x10000:
            out.extend((0xE0 | (cp >> 12), 0x80 | ((cp >> 6) & 63), 0x80 | (cp & 63)))
        else:
            out.extend((0xF0 | (cp >> 18), 0x80 | ((cp >> 12) & 63), 0x80 | ((cp >> 6) & 63), 0x80 | (cp & 63)))
    return out