Is the encoding method here different than other protobufs?

[kkailiwang]

My project takes in encoded proto strings (which were created from google's protobuf) and I just need a package that can decode them into javascript. Is this package's decoding process only for messages encoded by mapbox/pbf?

I ask because it works when I encode and then decode a message, like:
let pbf = new pbf(); pbf.writeString('hi'); pbf.finish(); return pbf.readString();

but not when I just decode a message (this is embedded):

let pbf = new Pbf();
pbf.writeRawMessage(dataString); 
pbf.finish();
//or just new Pbf(dataString)

const readFields = pbf.readFields(function(tag) { 
    const tagNeeded = tagArray[0];  
    if (tag === tagNeeded) {
        if (tagArray.length == 1) {
          return pbf.readFloat();
        }
        tagArray.splice(0, 1); 
        pbf.readMessage(readFields, {});
         
    }, {});
}