discourse/app/assets/javascripts/admin/addon/routes/admin-customize-email-style-edit.js

import { action } from "@ember/object";
import Route from "@ember/routing/route";
import { service } from "@ember/service";
import { i18n } from "discourse-i18n";

export default class AdminCustomizeEmailStyleEditRoute extends Route {
  @service dialog;

  model(params) {
    return {
      model: this.modelFor("adminCustomizeEmailStyle"),
      fieldName: params.field_name,
    };
  }

  setupController(controller, model) {
    controller.setProperties({
      fieldName: model.fieldName,
      model: model.model,
    });
    this._shouldAlertUnsavedChanges = true;
  }

  @action
  willTransition(transition) {
    if (
      this.get("controller.model.changed") &&
      this._shouldAlertUnsavedChanges &&
      transition.intent.name !== this.routeName
    ) {
      transition.abort();
      this.dialog.confirm({
        message: i18n("admin.customize.theme.unsaved_changes_alert"),
        confirmButtonLabel: "admin.customize.theme.discard",
        cancelButtonLabel: "admin.customize.theme.stay",
        didConfirm: () => {
          this._shouldAlertUnsavedChanges = false;
          transition.retry();
        },
      });
    }
  }
}