code: function get_module (id, env, strict) {
    var parsed = parse_id(id, env);
    var graph = parsed.graph;
    var mod = get_mod(parsed);
  
    var real_id = mod.main
      // if is main module, then use `pkg` as `real_id`
      ? parsed.k
      : parsed.id;
  
    // `graph` is the list of modules for a certain package
    var module = graph[real_id]
      // main module might be `require()`d as a relative path
      // inside the same package of the main module.
      // so we will fallback to `graph[parsed.id]``
      || graph[parsed.id];
  
    if (!module) {
      !strict || module_not_found(id);
      // So that `module` could be linked with a unique graph
      module = graph[real_id] = create_shadow_module(mod);
      module.graph = graph;
    }
  
    return module;
  }
docs: Get a shadow module or create a new one if not exists facade({ entry: 'a' })