Signal-Desktop/ts/util/enum.ts

31 lines
1.2 KiB
TypeScript

// Copyright 2021 Signal Messenger, LLC
// SPDX-License-Identifier: AGPL-3.0-only
/**
* Turn a string (like "green") into its enum type (like `Color.Green`). Useful when
* deserializing strings into enum types.
*
* It only supports enums with string values. It could theoretically support more, but:
*
* 1. It's easier to debug. A serialized value of "Green" is easier to associate with
* `Color.Green` than a serialized value of 2.
* 2. TypeScript's default uses numeric enum values. Because the stability of values is
* important and it's easy to mess up the stability of values (e.g., by reordering the
* enum), these are discouraged here.
*
* Again: no "hard" technical reason why this only supports strings; it's to encourage
* good behavior.
*/
export function makeEnumParser<
TEnumKey extends string,
TEnumValue extends string
>(
enumToParse: Record<TEnumKey, TEnumValue>,
defaultValue: TEnumValue
): (value: unknown) => TEnumValue {
const enumValues = new Set(Object.values(enumToParse));
const isEnumValue = (value: unknown): value is TEnumValue =>
typeof value === 'string' && enumValues.has(value);
return value => (isEnumValue(value) ? value : defaultValue);
}