Slack's new desktop application was launched for macOS. It was built using Electron for a faster, frameless look with a host of background improvements for a superior Slack experience. Instead of adopting a complete-in-box approach taken by other apps, Slack prefers a hybrid approach where some of the assets are loaded as part of the app, while others are made available remotely. Slack's original desktop app was written using the MacGap v1 framework using WebView to host web content within the native app frame. But it was difficult to upgrade with new features only available to Apple's WKWebView and moving to this view called for a total application rewrite.

Electron brings together Chromium's rendering engine with the Node.js runtime and module system. The new desktop app is now based on an ES6 + async/await React application is currently being moved gradually to TypeScript. Electron functions on Chromium's multi-process model, with each Slack team signed into a separate process and memory space. It also helps prevent remote content to directly access desktop features using a feature called WebView Element which creates a fresh Chromium renderer process and assigns rendering of content for its hosting renderer. Additional security can be ensured by preventing Node.js modules from leaking into the API surface and watching out for APIs with file paths. Communication between processes on Electron is carried out via electron-remote, a pared-down, zippy version of Electron's remote module, which makes implementing the web apps UI much easier.