jira_copy_summary: HTML encode summary for text/html

Userscript jira_copy_summary.user.js puts two kinds of content into
clipboard data: "text/plain" and "text/html".  Some users have reported
incorrect handling of Jira issue summaries with mentions of things which
look like HTML tags.  It causes such fake tags to be converted into line
breaks, when copy-pasted into rich text editors (like Slack's messages).

HTML encode issue summaries to handle angle brackets and other special
characters, which might be incorrectly interpreted as HTML syntax.

jira_copy_summary.user.js

@@ -1,7 +1,7 @@
 // ==UserScript==
 // @name         Jira copy summary
 // @namespace    https://github.com/rybak/atlassian-tweaks
-// @version      5.0
+// @version      5.1
 // @license      MIT
 // @description  Adds a "Copy summary" button for issue pages on Jira.
 // @author       Sergey Lukashevich, Andrei Rybak, Dmitry Trubin
@@ -36,6 +36,8 @@
  */
 
 /*
+version 5.1
+	- handling of ticket summaries with angle brackets "<>" has been fixed
 version 5.0
 	- Jira 9 is now supported in addition to versions 7 and 8.
 version 4.6
@@ -181,20 +183,35 @@ version 1.2
 		return div;
 	}
 
+	function htmlEncode(s) {
+		const tmp = document.createElement("div");
+		tmp.appendChild(document.createTextNode(s));
+		return tmp.innerHTML;
+	}
+
+	function getTextResult(ticketId, summaryText) {
+		return '[' + ticketId + '] ' + summaryText;
+	}
+
+	function getHtmlResult(ticketId, summaryText) {
+		const jiraUrl = getMeta("ajs-jira-base-url");
+		const fullLink = jiraUrl + "/browse/" + ticketId;
+		let htmlSummary = htmlEncode(summaryText);
+		if (cfg.get('italic_summary')) {
+			htmlSummary = '<i>' + htmlSummary + '</i> &#x200b;';
+		}
+		return '[<a href="' + fullLink + '">' + ticketId + '</a>] ' + htmlSummary;
+	}
+
 	function copyClickAction() {
-		var summaryText = document.getElementById("summary-val").textContent;
+		const summaryText = document.getElementById("summary-val").textContent;
 		var ticketIdSource = document.querySelector("#dx-issuekey-val-h1 a");
 		if (!ticketIdSource) {
 			ticketIdSource = document.querySelector(".aui-page-header-main .issue-link");
 		}
-		var ticketId = ticketIdSource.dataset.issueKey;
-		var jiraUrl = getMeta("ajs-jira-base-url");
-		var fullLink = jiraUrl + "/browse/" + ticketId;
-		textResult = '[' + ticketId + '] ' + summaryText;
-		if (cfg.get('italic_summary')) {
-			summaryText = '<i>' + summaryText + '</i> &#x200b;';
-		}
-		htmlResult = '[<a href="' + fullLink + '">' + ticketId + '</a>] ' + summaryText;
+		const ticketId = ticketIdSource.dataset.issueKey;
+		textResult = getTextResult(ticketId, summaryText);
+		htmlResult = getHtmlResult(ticketId, summaryText);
 		document.addEventListener('copy', handleCopyEvent);
 		document.execCommand('copy');
 		document.removeEventListener('copy', handleCopyEvent);