stokito/mail.html

## mail.html
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>EMail message parse in JavaScript sample</title>
    <script>
        function addHeader(header, headers) {
            if (header === "") {
                return
            }
            let headerValStart = header.indexOf(":")
            let headerKey = header.substring(0, headerValStart)
            let headerVal = header.substring(headerValStart + 1).trimStart()
            headers[headerKey] = headerVal
        }

        /**
         * @param {string} msgBody
         */
        function parseEnvelope(msgBody) {
            let headers = {}
            let lineStart = 0
            let header = ""
            for (let i = 0; i < msgBody.length; i++) {
                let lineEnd = msgBody.indexOf("\r\n", lineStart)
                if (lineEnd === -1) {
                    break
                }
                let line = msgBody.substring(lineStart, lineEnd)
                lineStart = lineEnd + 2 // skip CRLF
                if (line === "") {
                    addHeader(header, headers);
                    break
                }
                let lineTrim = line.trimStart()
                if (lineTrim.length < line.length) {
                    header += " " + lineTrim
                } else {
                    addHeader(header, headers);
                    header = line
                }
            }
            let body = msgBody.substring(lineStart)
            return {headers, body};
        }

        function parseMail() {
            let msgBody = document.getElementById("msgBody").value
            let {headers, body} = parseEnvelope(msgBody)
            console.log(headers)
            console.log(body)
            document.getElementById("from").innerText = headers["From"]
            document.getElementById("to").innerText = headers["To"]
        }
    </script>
</head>
<body>
<div>
    <button onclick="parseMail();">parse</button>
    <span id="from"></span>
    <span id="to"></span>
</div>
<textarea id="msgBody" style="width: 100%" rows="250">
MIME-Version: 1.0
From: Some Sender <sender@example.com>
Date: Mon, 16 May 2022 02:09:08 +0300
Subject: Greetings
To: recepient@example.com
Content-Type: text/plain; charset="UTF-8"

Hello
</textarea>

</body>
</html>
	<!DOCTYPE html>
	<html lang="en">
	<head>
	<meta charset="UTF-8">
	<title>EMail message parse in JavaScript sample</title>
	<script>
	function addHeader(header, headers) {
	if (header === "") {
	return
	}
	let headerValStart = header.indexOf(":")
	let headerKey = header.substring(0, headerValStart)
	let headerVal = header.substring(headerValStart + 1).trimStart()
	headers[headerKey] = headerVal
	}

	/**
	* @param {string} msgBody
	*/
	function parseEnvelope(msgBody) {
	let headers = {}
	let lineStart = 0
	let header = ""
	for (let i = 0; i < msgBody.length; i++) {
	let lineEnd = msgBody.indexOf("\r\n", lineStart)
	if (lineEnd === -1) {
	break
	}
	let line = msgBody.substring(lineStart, lineEnd)
	lineStart = lineEnd + 2 // skip CRLF
	if (line === "") {
	addHeader(header, headers);
	break
	}
	let lineTrim = line.trimStart()
	if (lineTrim.length < line.length) {
	header += " " + lineTrim
	} else {
	addHeader(header, headers);
	header = line
	}
	}
	let body = msgBody.substring(lineStart)
	return {headers, body};
	}

	function parseMail() {
	let msgBody = document.getElementById("msgBody").value
	let {headers, body} = parseEnvelope(msgBody)
	console.log(headers)
	console.log(body)
	document.getElementById("from").innerText = headers["From"]
	document.getElementById("to").innerText = headers["To"]
	}
	</script>
	</head>
	<body>
	<div>
	<button onclick="parseMail();">parse</button>
	<span id="from"></span>
	<span id="to"></span>
	</div>
	<textarea id="msgBody" style="width: 100%" rows="250">
	MIME-Version: 1.0
	From: Some Sender <sender@example.com>
	Date: Mon, 16 May 2022 02:09:08 +0300
	Subject: Greetings
	To: recepient@example.com
	Content-Type: text/plain; charset="UTF-8"

	Hello
	</textarea>

	</body>
	</html>