SSD1306 oled, clearing text line?

I use sdd1306 library:
I use mJS, the OLED display works fine.
My goal is to clear a text line rather than clear whole display with clearDiaplay().
I have tried:
to set colour to black with:
or change text background to black with second parameter:
d.setTextColor(Adafruit_SSD1306.WHITE, Adafruit_SSD1306.BLACK);
have tried just WHITE and BLACK without Adafruit_SSD1306.
White works, black does not. Got MJS callback error: [BLACK] is not defined.
I had a look in library and it looks like it is defined.
Any clue how to erase one text line please?
Thank you