Plugin Erasing Plus Signs In JS

I have this javascript code I added to the “text” area of the plugin settings, contained in <script> tags. Works great! Except sometimes it randomly does’t take plus signs (+) that I have in the javascript, where I’m concatenating some text string. Everything works great but that, why? Something with how the plugin reads in that “text” portion of the settings configuration. Please help.

https://wordpress.org/plugins/wp-splash-page/