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The Component Lifecycle


Part of what makes components so useful is that they let you take complete control of a section of the DOM. This allows for direct DOM manipulation, listening and responding to browser events, and using 3rd party JavaScript libraries in your Ember app.

As components are rendered, re-rendered and finally removed, Ember provides lifecycle hooks that allow you to run code at specific times in a component's life.

To get the most use out of a component, it is important to understand these lifecycle methods. The following hooks are a few of the most useful and commonly used in Ember apps.

Attaching to the Component Element

Suppose you want to integrate your favorite date picker library into an Ember project. Typically, 3rd party JS/jQuery libraries require a DOM element to bind to. So, where is the best place to initialize and attach the library?

After a component successfully renders its backing HTML element into the DOM, it will trigger its didInsertElement() hook.

Ember guarantees that, by the time didInsertElement() is called:

  1. The component's element has been both created and inserted into the DOM.
  2. The component's element is accessible via the component's $() method.

A component's $() method allows you to access the component's DOM element via jQuery. For example, you can set an attribute using jQuery's attr() method:

didInsertElement() {
  this.$().attr('contenteditable', true);
}

$() will, by default, return a jQuery object for the component's root element, but you can also target child elements within the component's template by passing a selector:

didInsertElement() {
  this.$('div p button').addClass('enabled');
}

Let's initialize our date picker by overriding the didInsertElement() method.

Date picker libraries usually attach to an <input> element, so we will use jQuery to find an appropriate input within our component's template.

didInsertElement() {
  this.$('input.date').myDatePickerLib();
}

didInsertElement() is also a good place to attach event listeners. This is particularly useful for custom events or other browser events which do not have a built-in event handler.

For example, perhaps you have some custom CSS animations trigger when the component is rendered and you want to handle some cleanup when it ends:

didInsertElement() {
  this.$().on('animationend', () => {
    $(this).removeClass('.sliding-anim');
  });
}

There are a few things to note about the didInsertElement() hook:

  • It is only triggered once when the component element is first rendered.
  • In cases where you have components nested inside other components, the child component will always receive the didInsertElement() call before its parent does.
  • Setting properties on the component in didInsertElement() triggers a re-render, and for performance reasons, is not allowed.
  • While didInsertElement() is technically an event that can be listened for using on(), it is encouraged to override the default method itself, particularly when order of execution is important.

Detaching and Tearing Down Component Elements

When a component detects that it is time to remove itself from the DOM, Ember will trigger the willDestroyElement() method, allowing for any teardown logic to be performed.

Component teardown can be triggered by a number of different conditions. For instance, the user may navigate to a different route, or a conditional Handlebars block surrounding your component may change:

{{#if falseBool}}
  {{my-component}}
{{/if}}

Let's use this hook to cleanup our date picker and event listener from above:

willDestroyElement() {
  this.$().off('animationend');
  this.$('input.date').myDatepickerLib().destroy();
}