Thank you @PitaJ for pointing me in the right direction. I adapted my code to the link you sent me.
(function (factory) { if (typeof module === 'object' && module.exports) { factory(require.main.require('benchpressjs')); } else { require(['benchpress'], factory); } }(function (Benchpress) { const logger = (data) => { console.log('Logger helper', data); return ''; }; const customHelpers = { register, logger, }; function register() { Object.keys(customHelpers).forEach(function (helperName) { Benchpress.registerHelper(helperName, customHelpers[helperName]); }); } register(); if (typeof module === 'object' && module.exports) { module.exports = customHelpers; } }));Just by doing this made it work client side. But then it stopped working server side. That was easily fixed though by running helpers.register in my library file.
const helpers = require('./lib/helpers'); helpers.register();Hope this helpes someone!