@alexlafroscia/ember-context NPM

@alexlafroscia/ember-context

Consume values from elsewhere in your Ember application

Compatibility

Ember.js v3.12 or above
Ember CLI v2.13 or above
Node.js v10 or above

Installation

ember install @alexlafroscia/ember-context

Usage

Ember Services are excellent for sharing global state across your application. However, there are many times where some state needs to be shared without it being considered global; it should be shared within a sub-tree of your application but thrown away once that sub-tree is no longer rendered.

To fill this gap, enter ember-context!

This addon is based on two related roles for a given value; a "Provider" and a "Consumer".

This "Provider" is always an instance of the ContextProvider component, which can be used like so:

<ContextProvider @key="shared-key" @value={{valueForSharedKey}}>
  {{! Consumer somewhere in here }}
</ContextProvider>

A "Consumer" can be either a usage of the consume-context helper or a component that injects the value as a property.

`consume-context`

The most basic -- and recommended -- usage is to consume a value using the consume-context helper. Using it might look like this:

{{consume-context "shared-key"}}

If placed beneath the ContextProvider in the example above, the helper will return valueForSharedKey. The beauty of this addon is that the helper can be anywhere in your template, as long as there is a ContextProvider with a key of shared-key somewhere above it, even across component boundaries.

`inject` Decorator

Additionally, for an experience closer to that of working with Ember services, you can add the inject decorator to your own components to consume a contextual value.

// app/components/my-component.js
import Component from '@glimmer/component';
import { inject as context } from '@alexlafroscia/ember-context';

export default class MyComponent extends Component {
  @context('shared-key') sharedKeyValue;
}

Similar to the consume-context helper, if MyComponent is rendered somewhere within ContextProvider with a @key of shared-key, the value of the sharedKeyValue on MyComponent will be valueForSharedKey. This allows you to avoid using the helper if it is not appropriate for your use-case.

Caveats

There are some potential issues around looking up the correct ContextProvider in certain circumstances that you should be aware of. Specifically, problems can arise if you use the same "key" for multiple providers and consume the value for that key within a conditional.

For your own safety, I recommend not rendering multiple providers for the same "key" simultaneously; if you can avoid that, things should work out okay!

If you do run into problems, please open an issue!.

Contributing

See the Contributing guide for details.

Prior Art

ember-provider: My first attempt at scoping state to a sub-tree of an application. It relied on actually walking up the component tree which, while more reliable, it not really possible with public Ember APIs. ember-context does not use any private APIs.
React Context: The original inspiration for the ability to set a value in one place in the tree and receive it elsewhere.