In hummus js how can i draw a filled rectangle with transparent?

How can I draw a rectangle with a transparent color?

I tried the below code. I am using hummusjs for modifying pdf.

cxt.drawRectangle(x,y,width,height,{type: 'fill',
           color: '#eeeeee',
           opacity: 0.9});  

from In hummus js how can i draw a filled rectangle with transparent?