How does Gio.Settings.bind_with_mapping method work in JavaScript

[undefined (MJ)]

I have been reading about bind_with_mapping method in JavaScript.

I want to persist preference settings like so:

this.settings = Gio.Settings.new("<app_id>");

this.settings.bind_with_mapping(
  "settings",
  this._comboRow,
  "selected",
  Gio.SettingsBindFlags.DEFAULT,
  (arg1, settingsVariant) => {
    const { model } = this._comboRow;

    for (let i = 0; i < model.get_n_items(); i++) {
      const stringObj = model.get_item(i);
      if (stringObj?.string === settingsVariant.unpack()) {
        this._comboRow.selected = i;
        return true;
      }
    }
   return true;
  },
  (selected, selectedVariantType) => {
    const stringObj = this._comboRow.model.get_item(selected);
    if (stringObj?.string) {
      return new GLib.Variant("s", stringObj.string);
    }
    return new GLib.Variant("s", 'HEX');
  }
);

When I select an item in the comboRow, the set_mapping callback(the second callback in the above example) is invoked and updates the settings correctly.

However, when I change the settings, I want the corresponding item in the ComboRow to be selected. The get_mapping callback(the first callback in the above example) is invoked with two arguments. The first argument is 0(I’m not even sure what it is). And the second argument is a GLib.Variant holding the settings. I can unpack and get the current settings.

I’m not sure how I can use that information passed as arguments to the get_mapping function to update the comboRow. You will notice I tried to update the comboRow’s selected property in the callback but it doesn’t work.

How does the get_mapping function work in JavaScript? I’ve read the original docs here and the corresponding descriptions for the callbacks:

• SettingsBindGetMapping
• SettingsBindSetMapping

The set_mapping function seems clear and straight forward but the get_mapping function is kinda confusing to me.