It is library that support Discord.js community! It will help you guys to convert those string that includes discord mentions string form to a simple ID!
You can simple install with this command here
npm install mention-converter
Detailed
const converter = require('mention-converter');
const result = converter('<@!123456789>', {detail: true})
// {"id": "123456789", detail: {type: "user", mobile: false}}
Simpled
const converter = require('mention-converter');
const result = converter('<@!123456789>')
// 123456789
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