void setInt16(int byteOffset, int value, [ Endianness endian = Endianness.BIG_ENDIAN ])

Sets the two bytes starting at the specified byteOffset in this object to the two's complement binary representation of the specified value, which must fit in two bytes.

In other words, value must lie between 215 and 215 - 1, inclusive.

Throws RangeError if byteOffset is negative, or byteOffset + 2 is greater than the length of this object.

Source 

void setInt16(int byteOffset, int value,
    [Endianness endian = Endianness.BIG_ENDIAN]);