There are two somewhat different approaches to using Smalltalk for the web. The first is Amber, which is more than four years old. It’s a fairly mature implementation of Smalltalk with good support. Amber is currently used in a number of places, including Sebastian Sastre’s living full-stack framework for the web known as flow.
Amber has had wider adoption thanks to its age. Users will get better support from the community. It is not obvious that PharoJS will still be around five years from now. The degree of adoption remains to be seen after PharoJS becomes production-ready.
If you’re interested in Amber, look at this tutorial trilogy.