Isolate output of right channel or left channel of audio blob using a panner (Javascript)

To isolate a channel of a signal with the Web Audio API you could use the ChannelSplitterNode which allows you to connect the individual channels of a signal separately.

A simple example to isolate the left channel (channel at index 0) from a stereo signal might look like this:

const channelSplitterNode = new ChannelSplitterNode(
    audioContext,
    { numberOfOutputs: 2 }
);

input
    .connect(channelSplitterNode)
    .connect(output, 0);

Jordan Eldredge once wrote a nice article which explains the difference between the StereoPannerNode and what he calls a StereoBalanceNode. Implementing a Robust Web Audio API Balance Node