const regex = /:[^:\s]+:|<:[^:\s]+:[0-9]+>|<a:[^:\s]+:[0-9]+>/g;
// Alternative syntax using RegExp constructor
// const regex = new RegExp(':[^:\\s]+:|<:[^:\\s]+:[0-9]+>|<a:[^:\\s]+:[0-9]+>', 'g')
const str = `TEMPLATES
--------------------------------------------------------------
:emote:
<:emote:189855563893571595>
<a:emote:18985556389571595>
OK MESSAGE
--------------------------------------------------------------
:emote:<:emote:189855563893571595><a:emote:189855563893571595>
BAD MESSAGE
--------------------------------------------------------------
:emote::asdf ::emote::: <:hey:>
<:a:emote:> hey
DOES IT WORK?
--------------------------------------------------------------
In the box below (click "Substitution" at the bottom if you can't see it) is all the characters that don't match the regex and will trigger your system to delete the message.`;
const subst = ``;
// The substituted value will be contained in the result variable
const result = str.replace(regex, subst);
console.log('Substitution result: ', result);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for JavaScript, please visit: https://developer.mozilla.org/en/docs/Web/JavaScript/Guide/Regular_Expressions