How to manage DOM element dependencies


I am trying to create a web-page where some elements (forms and buttons) become visible or are being hidden when some other elements (buttons) are clicked.
I try to find a way to manage this, that is re-usable, and easy to maintain.

My current solution is shown below, but I hope someone has a more elegant solution.
The problem with my own solution is that it will become difficult to read when the number of dependencies increase. It will then also require a lot of editing when I add another button and form.

My current solution is to use an observable to manage the state of the forms, like this:


  <button id="button-A">Show form A, hide button A and B</button>
  <button id="button-B">Show form B, hide button A and B</button>
  <form id="form-A">
    ...this form is initially hidden
    ...some form elements
    <button id="cancel-A">Hide form A, show button A and B</button>
  <form id="form-B">
    ...this form is initially hidden
    ...some form elements
    <button id="cancel-B">Hide form B, show button A and B</button>


  import 'dart:html';
  import 'package:observe/observe.dart';

  final $ = querySelector;
  final $$ = querySelectorAll;

  Map<String, bool> toBeObserved = {
    "showFormA" : false,
    "showFormB" : false

  // make an observable map
  ObservableMap observeThis = toObservable(toBeObserved);

  // start managing dependencies
  main() {
    // add click event to buttons
    ..onClick.listen((E) => observeThis["showFormA"] = true);
    ..onClick.listen((E) => observeThis["showFormB"] = true);

    // add click events to form buttons
    ..onClick.listen((E) {
      observeThis["showFormA"] = false;
    ..onClick.listen((E) {
      observeThis["showFormB"] = false;

    // listen for changes
    observeThis.changes.listen((L) {

      L.where((E) => E.key == 'showFormA').forEach((R) {
        $('#form-A').style.display = (R.newValue) ? 'block' : 'none';
        $('#button-A').style.display = (R.newValue || observeThis['showFormB']) ? 'none' : 'inline-block';
        $('#button-B').style.display = (R.newValue || observeThis['showFormB']) ? 'none' : 'inline-block';
      L.where((E) => E.key == 'showFormB').forEach((R) {
        $('#form-B').style.display = (R.newValue) ? 'block' : 'none';
        $('#button-A').style.display = (R.newValue || observeThis['showFormA']) ? 'none' : 'inline-block';
        $('#button-B').style.display = (R.newValue || observeThis['showFormA']) ? 'none' : 'inline-block';



You could use polymer’s template functionality like

<template if="showA">...

This should work without embedding your elements within Polymer elements too.
This discussion provides some information how to use <template> without Polymer elements.
Using Polymer elements could also be useful.
It all depends on your requirements/preferences.

Angular.dart is also useful for such view manipulation.

If you want to use plain Dart/HMTL I don’t have ideas how to simplify your code.

Answered By – Günter Zöchbauer

Answer Checked By – Mary Flores (FlutterFixes Volunteer)

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