OK so I figured it out - missing ()

Here is the working code for anyone else who wishes to use it.

Many thanks to all.

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var socket = new TCPSocket(false);
var result = "";
socket.onConnect = function()
{
socket.write("#pronto#@Z01@1$PLAY$~\r\n");
};

socket.onData = function()
{
var received=socket.read();
result += received;
CF.widget("LINE1").label="receiving"+ received;
};

socket.connect('192.168.1.100', 6789, 3000);