API overview

The public API is a nested object returned by await initialize(). It mirrors the Gmsh C API module tree, with one JavaScript method per C function.

Naming

C symbol → JS path, by stripping the gmsh prefix and lowercasing the first module segment:

gmshModelMeshGenerate   ->  gmsh.model.mesh.generate
gmshModelGeoAddPoint    ->  gmsh.model.geo.addPoint
gmshOptionSetNumber     ->  gmsh.option.setNumber
gmshLoggerGetLastError  ->  gmsh.logger.getLastError

Modules

JS path	Purpose
gmsh	initialize/finalize, open/merge/write/clear
gmsh.option	get/set numeric, string and colour options
gmsh.model	model entities, physical groups, boundary queries
gmsh.model.geo	built-in CAD kernel
gmsh.model.occ	OpenCASCADE CAD kernel (incl. STEP/IGES/BREP)
gmsh.model.mesh	mesh generation, queries, optimisation
gmsh.model.mesh.field	size fields
gmsh.logger	timing, memory, last error
gmsh.onelab	ONELAB parameter interface
gmsh.plugin	post-processing plugins
gmsh.parser	.geo parser access

GUI/visualization modules (fltk, graphics, view) are intentionally excluded — this build has no GUI.

Calling conventions

• Errors are thrown as JavaScript Errors (the C ierr is hidden).
• Scalar returns come back directly; output parameters come back as an object keyed by output name; nested outputs as arrays of arrays.
• Optional arguments may be omitted (their Gmsh defaults apply).
• (dim, tag) lists are flat number[] arrays: [dim0,tag0,dim1,tag1,...].

See Marshalling for the precise rules and the full API reference for every function.

Not exposed

• GUI/FLTK, OpenGL graphics, and on-screen post-processing views.

Mesh size callback

gmsh.model.mesh.setSizeCallback(fn) marshals a JS function into a native function-pointer callback that Gmsh invokes once per mesh vertex during mesh.generate(). It is the one function whose argument is a JS function rather than a plain value/array; see Marshalling.

Main-thread only. The callback's WebAssembly table slot lives in the instance that created it and is not visible to OpenMP worker pthreads, so it only works reliably with General.NumThreads set to 1 (Gmsh's default). Set a callback while multithreaded meshing is enabled and the runtime logs a one-time warning; workers invoking the slot during meshing may fail.