Serial Port Data Transfer on Javascript

Requirements
How to Proceed
The Code Example

An example of how to send and receive data from serial port on javascript with StrokeReader ActiveX. The code works with any RS232/RS485 ports and USB-to-serial adapters.

Requirements

Download and install the serial port interface ActiveX;
You need a browser that supports ActiveX (any version of Internet Explorer starting from version 11 is recommended).

How to Proceed

Paste the below code into a html file;
Check your Internet Explorer security settings to enable ActiveX execution.
Check the port number / baud rate / start-stop bit settings in the javascript code;
Check if your remote device requres specific DTR/RTS levels.

The Code Example

<!-- An example of controlling a serial port from JS with StrokeReader ActiveX -->
<html>
<head>
<script type="text/javascript">
var port;

function SetPort() 
{ 
	port = document.getElementById("comport");
	port.Port = 1;  //COM1
	port.BaudRate = 9600;
	port.DataBits = 8;
	port.Parity = 0; //NOPARITY
	port.StopBits = 0; //one stop bit

	port.Connected = 1; 
	
	if(port.Error > 0)
		alert(port.ErrorDescription);
}

function SendData()
{ 
	s = new Array(0x01, 0x20, 0x40, 0x80, 0xFF);  //Sending an array of bytes
	port.Send(s);
	
	port.Send("ABCDE"); //Sending a text string
}

function RTS_click()
{
	rts = document.getElementById("rts");
	port.RTS = rts.checked;
}
function DTR_click()
{
	dtr = document.getElementById("dtr");
	port.DTR = dtr.checked;
}

function Disconnect()
{
	port.Connected = 0;
}

function Connect()
{
	port.Connected = 1;
}

function port_list()
{
	ports = port.PortsAvailable.split(",");
	s = "";
	for (i = 0; i<ports.length; i++)
		s += port.GetPortFriendlyName(ports[i]) + "\n";
	alert(s);
}
</script>

<script for="comport" event="CommEvent(Evt, Data)">
	port =  document.getElementById("comport");
	connected =  document.getElementById("connected");
	cts =  document.getElementById("cts");
	dsr =  document.getElementById("dsr");
	output = document.getElementById("output");

	if(Evt==3) //=EVT_CONNECT
	{
		connected.checked = true;
	}
	if(Evt==0) //=EVT_DISCONNECT
	{
		connected.checked = false;
	}
	if(Evt==2) //EVT_SERIALEVENT
	{
		if(Data&0x0008)
		{
			cts.checked = port.CTS;
		}
		if(Data&0x0010)
		{
			dsr.checked = port.DSR;
		}
	}	
	if(Evt==1) //=EVT_DATA
	{ 
		var a = port.Read(2); //BINARYJS
		if(typeof a==="undefined")
			return;
		s = "";
		arr = new VBArray(a).toArray();
		for (i = 0; i<arr.length; i++)
			s += " " + arr[i].toString(16);
		output.value += s;
	}
</script>
</head>

<body onload="SetPort()">  
	<object classid="CLSID:7E42B8C5-73BE-4806-8904-FF4080A696EC" id="comport"></object>

	<button onclick="javascript:SendData()">Send</button>
	<button onclick="javascript:Disconnect()">Disconnect</button>
	<button onclick="javascript:Connect()">Connect</button>
	<button onclick="javascript:port_list()">Port list</button>
	<input type="checkbox" id="rts" onClick="RTS_click()">RTS</input>
	<input type="checkbox" id="dtr" onClick="DTR_click()">DTR</input>
	<br>
	<input type="checkbox" disabled="disabled" id="connected">Connected</input>
	<input type="checkbox" disabled="disabled" id="cts">CTS</input>
	<input type="checkbox" disabled="disabled" id="dsr">DSR</input>
	<br>
	<textarea id="output" rows=10 cols=50></textarea>

</body>
</html>

© 2026 StrokeScribe. All rights reserved. Use of any portion of this site constitutes acceptance of our Terms of Use and Privacy Policy. The website material may not be reproduced, except with the prior written permission.

Serial Port Data Transfer on Javascript

Table of Contents

Requirements

How to Proceed

The Code Example