We may want to use Javascript to apply the same behaviour to multiple modules or components.

For example, we may use a Collapser constructor that toggles an element’s visibility.

There are two approaches we can take, both of which complement the CSS approach we’ve discussed in previous chapters.

1. Encapsulating state to the module

To do this, we would need to specify a module-specific state class to the constructor as follows:

var module1Collapser = new Collapser(element1, {
  cssHideClass: 'moduleA-isHidden'

var module2Collapser = new Collapser(element2, {
  cssHideClass: 'moduleB-isHidden'

Then reuse the CSS styles as follows:

.moduleB-isHidden {
  display: none;

The trade-off is that this list could grow quickly (or use a mixin). And every time we add behavior, we need to update the CSS. A small change, but a change nonetheless. In this case we might consider a global state class.

2. Creating a global state class

If we find ourselves repeating the exact same set of styles for multiple modules, it might be better to use a global state class as follows:

.globalState-isHidden {
  display: none;

This approach does away with the long comma-delimited list. And we no longer need to specify the module class when instantiating. This is because the global class will be referenced from within.

var module1Collapser = new Collapser(element1);
var module2Collapser = new Collapser(element2);

However, this approach doesn’t always make sense. We may have two different modules that behave the same, but look different, which is something we’ve discussed in State.

3. The best of both worlds

We could combine the two approaches by defaulting the class to the global state class. And then only when needed we can specify a class during instantiation as shown in the first example above.

Final thought

When we think about state, particularly with our Javascript hat on, we need to consider how this state affects behaviour as well as style. Different components may share the same behaviour, but they may look rather different. After careful consideration, we can choose the right solution to the problem.


  1. Introduction
  2. Semantics
  3. Reuse
  4. IDs
  5. Conventions
  6. Modules
  7. State
  8. Modifiers
  9. Versioning
  10. Javascript
  11. Organisation
  12. FAQs

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