Steps to reproduce:

1. Install Zabbix Server LTS 5.0
2. Download media_slack.xml from https://www.zabbix.com/ru/integrations/slack(), but you need download from source (sic), because in Zabbix Server(frontend) 5.0 yaml is unsupported extension
3. Import new media type
4. Click test + send test

Result:
Details Media type test failed.
SyntaxError: unterminated statement (line 116)
Expected:
Success

It happened because single quote not escaped.
this (x2)

 throw 'Can't process event tags: ' + error;


to

 throw 'Can\'t process event tags: ' + error;


https://git.zabbix.com/projects/ZBX/repos/zabbix/browse/templates/media/slack/media_slack.xml?at=refs%2Ftags%2F5.0.16#268
https://git.zabbix.com/projects/ZBX/repos/zabbix/browse/templates/media/slack/media_slack.xml?at=refs%2Ftags%2F5.0.16#234