Pas2JS allows developers to combine web and desktop development by transpiling Pascal code to JavaScript. It can transpile entire projects, modules, and files from Pascal to JavaScript. This allows developers to write code in Pascal and generate JavaScript files that can run in browsers or Node.js. The presentation demonstrated using Pas2JS from the command line, as a library, and with Electron. It also showed integrating JavaScript and Pascal using JS1Pas and calling Pascal code from JavaScript in a hybrid app.