How to properly handle incoming TCP/UDP data

After checking out suggestions from @maze1980 and @Robin, I've created my TCP message handler, and it kinda works. I appear to be getting data corruption in the buffer that I copy the incoming data into, and I can't figure out what I'm doing wrong. The handler:

if(this.tcpBuffer && this.tcpBuffer.byteLength) {
    let leftoverDataLen = this.tcpBuffer.byteLength;
    let tmpBuffer = new Uint8Array(leftoverDataLen + chunk.length);
    tmpBuffer.set(this.tcpBuffer, 0);
    tmpBuffer.set(E.toUint8Array(chunk), leftoverDataLen);
    this.tcpBuffer = tmpBuffer;
}
else {
    this.tcpBuffer = E.toUint8Array(chunk);
}

So I either start off with a brand new copy of the incoming data (converted to Uint8Array), or I append the new data to the end of the current buffer. When done, this.tcpBuffer should contain all of the data that I've not yet processed. Am I doing this correctly / is there a better way to append the data?