Example youtrack workflow. It notifies some user about new mentions in comments.

slack-comment-workflow-multiple.js

var entities = require('@jetbrains/youtrack-scripting-api/entities');
var http = require('@jetbrains/youtrack-scripting-api/http');

var slackIdByUsername = {}

slackIdByUsername['@person1'] = '{person1_slack_id}';
slackIdByUsername['@person2'] = '{person2_slack_id}';
slackIdByUsername['@person3'] = '{person3_slack_id}';

var webhookUrl = 'https://{slack_webhook_url}';
var webhookTimeout = 2000;

exports.rule = entities.Issue.onChange({
  title: 'Send notification to slack when one of users is mentioned in comment',
  guard: function (ctx) {
    return ctx.issue.comments.added.isNotEmpty()
  },
  action: function (ctx) {
    ctx.issue.comments.added.forEach(function (comment) {
      var text = comment.text;
      var mentioned = [];
      for (var username in slackIdByUsername) {
        if (text.indexOf(username) !== -1) {
          mentioned.push(username)
        }
      }
      if (mentioned.length === 0) {
        return;
      }
      
      var mentionedForSlack = mentioned.map(function (username) {
        return '<@' + slackIdByUsername[username] + '>';
      });

      var issue = ctx.issue;
      var pretext = "New mention on issue <" + issue.url + "|" + issue.id + ">";
      var slackText = "Hey, " + mentionedForSlack.join(", ") + "!\nThere is a new mention in comment:\n" + text;

      var payload = {
        "attachments": [{
          "fallback": "New mention on issue " + issue.id,
          "pretext": pretext,
          "text": slackText,
          "color": issue.fields.Priority.backgroundColor
        }]
      };
            
      var webhook = new http.Connection(webhookUrl, null, webhookTimeout);
      var response = webhook.postSync('', null, JSON.stringify(payload));
      if (!response.isSuccess) {
        console.warn('Failed to post notification to Slack. Details: ' + response.toString());
      } else {
        console.log("Comment(" + comment.url + ") notified to slack by WebHook(" + webhookUrl + ")");
      }
    });
  },
  requirements: {}
});

slack-comment-workflow.js

var entities = require('@jetbrains/youtrack-scripting-api/entities');
var http = require('@jetbrains/youtrack-scripting-api/http');

var username = '@person';
var slackId = '{person_slack_id}';
var webhookUrl = 'https://{slack_webhook_url}';
var webhookTimeout = 2000;

exports.rule = entities.Issue.onChange({
  title: 'Send notification to slack when ' + username + ' is mentioned in comment',
  guard: function (ctx) {
    return ctx.issue.comments.added.isNotEmpty()
  },
  action: function (ctx) {
    ctx.issue.comments.added.forEach(function (comment) {
      var text = comment.text;
      if (text.indexOf(username) === -1) {
        return;
      }

      var issue = ctx.issue;
      var pretext = "New mention on issue <" + issue.url + "|" + issue.id + ">";
      var slackText = "Hey, <@" + slackId + ">!\nThere is a new mention in comment:\n" + text;

      var payload = {
        "attachments": [{
          "fallback": "New mention on issue " + issue.id,
          "pretext": pretext,
          "text": slackText,
          "color": issue.fields.Priority.backgroundColor
        }]
      };
            
      var webhook = new http.Connection(webhookUrl, null, webhookTimeout);
      var response = webhook.postSync('', null, JSON.stringify(payload));
      if (!response.isSuccess) {
        console.warn('Failed to post notification to Slack. Details: ' + response.toString());
      } else {
        console.log("Comment(" + comment.url + ") notified to slack by WebHook(" + webhookUrl + ")");
      }
    });
  },
  requirements: {}
});