To build web clients in Smalltalk that run at speed close to native JavaScript, we need a transpiler to perform source to source conversion from Smalltalk to JavaScript. For a good user experience, Smalltalk developers should be able to work as they usually do with any application, and fully use the Smalltalk kernel and core libraries. This experience relies on the assumption made by developers that the Smalltalk language contracts are met. However, we also want to be pragmatic and enable reuse of the existing JavaScript ecosystem with code built in Smalltalk. JavaScript code generated from Smalltalk transpilation should seamlessly integrate with code natively developed in JavaScript. In this paper, we address these two issues focusing on language kernels. We present solutions to address differences between Smalltalk and JavaScript kernels to enable both the best Smalltalk developer experience while leveraging the JavaScript ecosystem.