@ember/render-modifiers

Provides element modifiers that can be used to hook into specific portions of the rendering lifecycle.

When to use these modifiers (and when not to use them)

The modifiers provided in this package are ideal for quickly migrating away from classic Ember components to Glimmer components, because they largely allow you to use the same lifecycle hook methods you've already written while attaching them to these modifiers. For example, a didInsertElement hook could be called by {{did-insert this.didInsertElement}} to ease your migration process.

However, we strongly encourage you to take this opportunity to rethink your functionality rather than use these modifiers as a crutch. In many cases, classic lifecycle hooks like didInsertElement can be rewritten as custom modifiers that internalize functionality manipulating or generating state from a DOM element. Other times, you may find that a modifier is not the right fit for that logic at all, in which case it's worth revisiting the design to find a better pattern.

Either way, we recommend using these modifiers with caution. They are very useful for quickly bridging the gap between classic components and Glimmer components, but they are still generally an anti-pattern. We recommend considering a custom modifier in most use-cases where you might want to reach for this package.

Compatibility

• Ember.js v2.18 or above
• Ember CLI v2.13 or above

Installation

ember install @ember/render-modifiers

Usage Examples

Example: Scrolling an element to a position

This sets the scroll position of an element, and updates it whenever the scroll position changes.

Before:

{{yield}}

export default Component.extend({
  classNames: ['scroll-container'],

  didRender() {
    this.element.scrollTop = this.scrollPosition;
  }
});

After:

<div
  {{did-insert this.setScrollPosition @scrollPosition}}
  {{did-update this.setScrollPosition @scrollPosition}}

  class="scroll-container"
>
  {{yield}}
</div>

export default class Component.extend({
  setScrollPosition(element, [scrollPosition]) {
    element.scrollTop = scrollPosition;
  }
})

Example: Adding a class to an element after render for CSS animations

This adds a CSS class to an alert element in a conditional whenever it renders to fade it in, which is a bit of an extra hoop. For CSS transitions to work, we need to append the element without the class, then add the class after it has been appended.

Before:

{{#if this.shouldShow}}
  <div class="alert">
    {{yield}}
  </div>
{{/if}}

export default Component.extend({
  didRender() {
    let alert = this.element.querySelector('.alert');

    if (alert) {
      alert.classList.add('fade-in');
    }
  }
});

After:

{{#if this.shouldShow}}
  <div {{did-insert this.fadeIn}} class="alert">
    {{yield}}
  </div>
{{/if}}

export default Component.extend({
  fadeIn(element) {
    element.classList.add('fade-in');
  }
});

Example: Resizing text area

One key thing to know about {{did-update}} is it will not rerun whenever the contents or attributes on the element change. For instance, {{did-update}} will not rerun when @type changes here:

<div {{did-update this.setupType}} class="{{@type}}"></div>

If {{did-update}} should rerun whenever a value changes, the value should be passed as a parameter to the modifier. For instance, a textarea which wants to resize itself to fit text whenever the text is modified could be setup like this:

<textarea {{did-update this.resizeArea @text}}>
  {{@text}}
</textarea>

export default Component.extend({
  resizeArea(element) {
    element.style.height = `${element.scrollHeight}px`;
  }
});

Example: ember-composability-tools style rendering

This is the type of rendering done by libraries like ember-leaflet, which use components to control the rendering of the library, but without any templates themselves. The underlying library for this is here. This is a simplified example of how you could accomplish this with Glimmer components and element modifiers.

Node component:

// components/node.js
export default Component.extend({
  init() {
    super(...arguments);
    this.children = new Set();

    this.parent.registerChild(this);
  }

  willDestroy() {
    super(...arguments);

    this.parent.unregisterChild(this);
  }

  registerChild(child) {
    this.children.add(child);
  }

  unregisterChild(child) {
    this.children.delete(child);
  }

  didInsertNode(element) {
    // library setup code goes here

    this.children.forEach(c => c.didInsertNode(element));
  }

  willDestroyNode(element) {
    // library teardown code goes here

    this.children.forEach(c => c.willDestroyNode(element));
  }
}

<!-- components/node.hbs -->
{{yield (component "node" parent=this)}}

Root component:

// components/root.js
import NodeComponent from './node.js';

export default NodeComponent.extend();

<!-- components/root.hbs -->
<div
  {{did-insert (action this.didInsertNode)}}
  {{will-destroy (action this.willDestroyNode)}}
>
  {{yield (component "node" parent=this)}}
</div>

Usage:

<Root as |node|>
  <node as |node|>
    <node />
  </node>
</Root>

License

This project is licensed under the MIT License.