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Add an interface Database #3511

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Merged
merged 4 commits into from
Jul 30, 2020
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Add an interface Database #3511

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22ab777
Add an interface Database
Feiyang1 Jul 29, 2020
1c3ed6b
Create thirty-flies-flow.md
Feiyang1 Jul 29, 2020
7dc980b
Update .changeset/thirty-flies-flow.md
Feiyang1 Jul 29, 2020
12f8c00
Update thirty-flies-flow.md
Feiyang1 Jul 30, 2020
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6 changes: 6 additions & 0 deletions .changeset/thirty-flies-flow.md
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Original file line number Diff line number Diff line change
@@ -0,0 +1,6 @@
---
"@firebase/database-types": patch
"@firebase/database": patch
---

Added interface `Database` which is implemented by `FirebaseDatabase`. This allows consumer SDKs (such as the Firebase Admin SDK) to export the database types as an interface.
11 changes: 9 additions & 2 deletions packages/database-types/index.d.ts
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Expand Up @@ -32,9 +32,16 @@ export interface DataSnapshot {
val(): any;
}

export class FirebaseDatabase {
private constructor();
export interface Database {
app: FirebaseApp;
goOffline(): void;
goOnline(): void;
ref(path?: string | Reference): Reference;
refFromURL(url: string): Reference;
}

export class FirebaseDatabase implements Database {
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Since this is a .d.ts file, isn't "class" already considered an interface? Could we just drop private constructor?

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IIUC, we use it to type the actual class that we export and we don't want people to instantiate it, so private constructor is important. Please correct me if i'm wrong.

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@Feiyang1 Feiyang1 Jul 29, 2020 •
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You can use d.ts file to annotate a JS library. It tells Typescript that the JS library exports a class that people can import and use. People can actually do this and Typescript allows it:

import {FirebaseDatabase} from '@firebase/database-types';

new FirebaseDatabase(); // if not having the private constructor

For this reason, I consider it as a bad practice to use class instead of interface in our types packages, if you are just going for the instance type.

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If I understand this correctly, it seems like the following two are equivalent:

export class Foo {
  private constructor();
  foo: string;
}

export interface Foo {
 foo: string;
}

If so, can we drop the existing class declaration? If not, this LGTM.

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@Feiyang1 Feiyang1 Jul 30, 2020 •
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They are the same for representing the instance type, but we need the constructor type which requires a class type. See https://github.com/firebase/firebase-js-sdk/blob/master/packages/database/index.ts#L97

I believe it is to allow people to do instanceof, but disallow newing an object, so we need to keep the class type.

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Yeah, the instanceof check was the only thing that I could think of, but it seemed a bit unlikely. Better not to break anyone though.

private constructor();
app: FirebaseApp;
goOffline(): void;
goOnline(): void;
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2 changes: 1 addition & 1 deletion packages/database/index.node.ts
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Expand Up @@ -85,7 +85,7 @@ export function initStandalone(app: FirebaseApp, url: string, version: string) {
app,
authProvider,
url
) as types.FirebaseDatabase,
) as types.Database,
namespace: {
Reference,
Query,
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