export_gltf_on_save.py

import bpy
from bpy.app.handlers import persistent
import os


# This method will select everything, apply all the transforms,
# export and then undo both (transform apply and select all).
@persistent
def VY__export_models(file):
    bpy.ops.object.select_all(action='SELECT')
    bpy.ops.ed.undo_push(message = "SELECT ALL - SCRIPT")
    bpy.ops.object.transform_apply(location=True, rotation=True, scale=True)
    bpy.ops.ed.undo_push(message = "APPLY EVERYTHING - SCRIPT!")
    # https://docs.blender.org/api/current/bpy.ops.export_scene.html#bpy.ops.export_scene.gltf
    bpy.ops.export_scene.gltf(
        filepath=bpy.path.abspath("//models.glb"),
        export_format='GLB',
        use_active_collection=False,
        export_apply=True,
        use_visible=True,
    )
    bpy.ops.ed.undo()
    bpy.ops.ed.undo()
    

# A list containing our methods for the save_post handler.   
save_post_operators= [
    VY__export_models,
]

# List containing the method names.
save_post_operators_names = [v.__name__ for v in save_post_operators]

# Remove existing handler matching the methods (if any) so we don't have 
# duplications.
for f in bpy.app.handlers.save_post:
    if f.__name__ in save_post_operators_names:
        bpy.app.handlers.save_post.remove(f)

# Then add the operators
# https://docs.blender.org/api/current/bpy.app.handlers.html
for f in save_post_operators:
    bpy.app.handlers.save_post.append(f)