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feat(types): turn LocalForageWrapper into a generic class #528

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feat(types): turn LocalForageWrapper into a generic class #528

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20 changes: 9 additions & 11 deletions src/storageWrappers/LocalForageWrapper.ts
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Original file line number Diff line number Diff line change
@@ -1,22 +1,23 @@
import { PersistentStorage } from '../types';

export class LocalForageWrapper
implements PersistentStorage<string | object | null> {
export class LocalForageWrapper<T = string | object | null>
implements PersistentStorage<T>
{
protected storage;

constructor(storage: LocalForageInterface) {
constructor(storage: LocalForageInterface<T>) {
this.storage = storage;
}

getItem(key: string): Promise<string | null> {
getItem(key: string): Promise<T | null> {
return this.storage.getItem(key);
}

removeItem(key: string): Promise<void> {
return this.storage.removeItem(key);
}

setItem(key: string, value: string | object | null): Promise<void> {
setItem(key: string, value: T | null): Promise<void> {
return new Promise((resolve, reject) => {
this.storage
.setItem(key, value)
Expand All @@ -26,12 +27,9 @@ export class LocalForageWrapper
}
}

interface LocalForageInterface {
export interface LocalForageInterface<T = string | object | null> {
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I exported LocalForageInterface here as it could be useful.

I'm currently writing a wrapper for LocalForageWrapper that compresses the cache into a binary, so I need both the generic class and the interface here because I need to use composition over inheritance to be able to turn LocalForageWrapper into PersistentStorage<Uint8Array>, but make sure the newly created wrapper exposes string.

// Actual type definition: https://github.com/localForage/localForage/blob/master/typings/localforage.d.ts#L17
getItem(key: string): Promise<string | null>;
setItem(
key: string,
value: string | object | null,
): Promise<string | object | null>;
getItem(key: string): Promise<T | null>;
setItem(key: string, value: T | null): Promise<T | null>;
removeItem(key: string): Promise<void>;
}