A method of cross-compiling FORTRAN code to WebAssembly with LLVM and flang is described. only numerical computation is supported, standard library currently cannot be used. In spite of this limitation, it already enabled a non-trivial practical application: cross-compiling the TNT-MMTL 2D electromagnetic field solver to WebAssembly, allowing electronics designers to solve microwave transmission lines using the Boundary Element Method (BEM) without leaving the Web browser.| niconiconi.neocities.org