Ember.js Octane vs Classic Cheat Sheet

In classic Ember, ember generate component created three files: the template, a JavaScript file, and a test. In Octane, ember generate component skips creating the JavaScript file. If you want the backing JavaScript class as well, include the -gc option.

The location of component templates has changed in Octane. This is known as "template co-location."

Angle brackets are a way to invoke components in a template file. There's no change in behavior. Learn more about features and using codemods to update your existing components.

Angle brackets components can be used as either inline or block components. There's no change in behavior. {{yield}} looks and works the same. Learn more about features and using codemods to update your existing components.

You can nest components in your file structure, and use them in a template with angle brackets invocation. There's no change in behavior.

If a property was received from a parent component, refer to it with an @. There's no change in behavior. (Visit the Ember Guides to learn more.)

If a property is defined in the JavaScript file for this component's template, use this when you refer to it. There's no change in behavior. Learn more about features and using codemods to update your existing components.

When you pass an argument to a component, use an @ symbol on the left hand side. There's no change in behavior. Learn more about features and using codemods to update your existing components.

If a property is coming from a template's own JavaScript file, remember to put a this before it and wrap it in curly braces. Learn more about features and using codemods to update your existing components.

In Octane, components don't have a default wrapper anymore, so you don't need tagName! Just put the tag right in the template.

Since components are tagless, there's no elementId, but you can generate your own. This is especially helpful for creating accessible forms.

An Octane component imports from the @glimmer package namespace. It also uses native class syntax. Glimmer components have different API methods than classic components. If you aren't familiar with native classes, first check out the documentation on MDN. Then, learn more about Glimmer components from the Ember.js Guides and the API Reference.

Properties follow native JavaScript class syntax. No commas!

Octane components enforce "Data Down, Actions Up." When data is passed down to a component, the only way to change that data is to call an action that was passed in too. In another words, there is no two-way binding for component arguments.

In Octane, arguments are set on the args property, this.args. They are not set on the class instance, this. As a result, you can distinguish internal class values from external arguments. (Visit the Ember Guides to learn more about arguments.)

Octane components do not use this.get or this.set. Access and modify properties directly, the same as you would in a regular JavaScript class.

Label the properties that should be tracked. Getters will be updated automatically.

In Octane, it is recommended to rewrite a computed property as tracked property. In case that isn't possible (maybe you need caching), the @computed decorator is available.

In the JavaScript class, use the @action decorator to mark the function that you want to call from the template. In the template, use the {{on}} modifier to decide when to call the function. If you need to pass an argument to the function, use {{fn}} helper too. (Visit the Ember Guides to learn more.)

Because an argument is read-only, you cannot set its default value in the consuming class. Instead, you can create a getter to wrap the argument and provide the default value.

You cannot use mixins on anything that uses native class syntax (e.g. components that import from @glimmer/component). The migration strategy depends on your use case. If your app depends on an addon that uses mixins, it may be best to continue using classic components until the addon is Octane-ready.

constructor comes from native JavaScript class. You can use this hook to set up the component class, similarly to what you might have done in init. (Visit the Ember Guides to learn more about constructor and super.)

willDestroy is the only other lifecycle hook (besides constructor) that Glimmer components have. You can use this hook to tear down the component class, similarly to what you might have done in willDestroyElement. (Visit the Ember Guides to learn more about lifecycle of Glimmer components.)

If you install @ember/render-modifiers, you get {{did-insert}} and {{did-update}} modifiers. You may use them to replace a classic component's lifecycle hooks didInsertElement, didRender, and didUpdate.

If you used the didInsertElement hook, consider making an action. You can call the action with the {{did-insert}} modifier. Use the @action decorator to bind the correct context (this). (Visit the Ember Guides to learn more about lifecycle of Glimmer components.)

In a route template, the model comes from an outside context. Use @model to access the result from the route's model hook.