In the B4X developing suite, B4J is used to develop desktop apps based on JavaFX or server apps based on Jetty. By default, it cannot be used to create web applications without a server. A third-party library, BANano, makes this possible. It can transpile everything you write in B4J to Javascript, HTML, and CSS. The project can run purely in the browser.
Dynamsoft Barcode Reader is written in C++. It provides a JavaScript version that uses WebAssembly. The barcode decoding can be done on the client-side, which is a good match for BANano.