Created
April 28, 2019 16:39
-
-
Save benfluleck/e43b195b881e17b22a82f5fd59a08155 to your computer and use it in GitHub Desktop.
Dependency Inversion
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
// BAD | |
class InventoryRequester { | |
constructor() { | |
this.REQ_METHODS = ['HTTP']; | |
} | |
requestItem(item) { | |
// ... | |
} | |
} | |
class InventoryTracker { | |
constructor(items) { | |
this.items = items; | |
// BAD: We have created a dependency on a specific request implementation. | |
// We should just have requestItems depend on a request method: `request` | |
this.requester = new InventoryRequester(); | |
} | |
requestItems() { | |
this.items.forEach((item) => { | |
this.requester.requestItem(item); | |
}); | |
} | |
} | |
const inventoryTracker = new InventoryTracker(['apples', 'bananas']); | |
inventoryTracker.requestItems(); | |
// GOOD | |
class InventoryTracker { | |
constructor(items, requester) { | |
this.items = items; | |
this.requester = requester; | |
} | |
requestItems() { | |
this.items.forEach((item) => { | |
this.requester.requestItem(item); | |
}); | |
} | |
} | |
class InventoryRequesterV1 { | |
constructor() { | |
this.REQ_METHODS = ['HTTP']; | |
} | |
requestItem(item) { | |
// ... | |
} | |
} | |
class InventoryRequesterV2 { | |
constructor() { | |
this.REQ_METHODS = ['WS']; | |
} | |
requestItem(item) { | |
// ... | |
} | |
} | |
// By constructing our dependencies externally and injecting them, we can easily | |
// substitute our request module for a fancy new one that uses WebSockets. | |
const inventoryTracker = new InventoryTracker(['apples', 'bananas'], new InventoryRequesterV2()); | |
inventoryTracker.requestItems(); |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment