void setInt8(int byteOffset, int value)

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

In other words, value must be between -128 and 127, inclusive.

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

Source

void setInt8(int byteOffset, int value);