recorderjs change from stereo to mono while recording wav files

I am using recorderjs to record audio files in .wav format. The output wav file is of 44100Khz with Stereo Channel. But my requirement is to record the files with Mono Channel 44100Khz.

I guess encodeWAV function here is making the wav files in stereo channel, but not sure how to change it so that the files comes in mono format. I tried to make numChannels =1. But still its coming in Stereo format. Is there any other js library to record in such audio format?