The library has both imperative and declarative mechanisms for reading bits- The BitstreamReader class provides all the read*() methods and the elements provide a way to declare fields (ie "structural"), and use BitstreamReader to accomplish that.

For bitstreamReader.read(), the first parameter is the number of bits to read. So for example:

    import { BitstreamReader } from '@astronautlabs/bitstream';
    let reader = new BitstreamReader();
    reader.addBuffer(Buffer.from([0b11101010, 0b10000000]));
    let value = reader.readSync(9);
    expect(value).to.equal(0b111010101);

Conversely for writing with BitstreamWriter you can do:

    import { BufferedWritable, WritableStream } from '@astronautlabs/bitstream';
    let writable = new BufferedWritable();
    let writer = new BitstreamWriter(writable);
    writer.write(9, 0b111010101);
    expect(writable.buffer.length).to.equal(1); // because the last bit isn't a full byte
    writer.write(7, 0);
    expect(writable.buffer.length).to.equal(2);
    expect(Array.from(writable.buffer)).to.eql([0b11101010, 0b10000000]);
    

Using Bitstream Elements you would do

    import { BitstreamElement } from '@astronautlabs/bitstream';
    class MyElement extends BitstreamElement {
        @Field(9) value : number;
    }

    expect(MyElement.deserialize(Buffer.from([0b11101010, 0b10000000])).value).to.equal(0b111010101) // with 7 bits left
    expect(Array.from(new MyElement().with({ value: 0b111010101 }).serialize())).to.eql([0b11101010, 0b10000000])