V8 adds the arrow function declarator from modern JavaScript. This is a handy shorthand but it’s more than just that. There are some behavioral differences too that you’ll need to understand before diving in. The old way of declaring functions still exists of course, and there will always be a need for it.
More tips and guidance from Bruce Mcpherson for developers migrating code to the Apps Script V8 runtime.
Source: JavaScript V8 Arrow functions, this and that – Desktop liberation
Member of Google Developers Experts Program for Google Workspace (Google Apps Script) and interested in supporting Google Workspace Devs.