type ExtendsFrom<Type, Subtype extends Parent> = Subtype;
I'm assuming I'm missing something because this feels like a basic type but I haven't figured out how I can replicate this functionality with the built in Utility types or any of the types in typefest.
It's basically just a type intersection with better error reporting.
A couple of examples of when this could be useful:
// Type-safe string union subset
type AllowedValues = 'foo' | 'bar' | 'baz';
// we get eager type errors if one of the values specified in
// this string union does not appear in AllowedValues.
type RestrictedAllowedValues = ExtendsFrom<AllowedValues, 'foo' | 'bar'>
// Constraining config value types
type ConfigKeys = 'blah' | 'blah2';
type AllowedValue = string | boolean | number;
type BaseConfig = {
[key in ConfigKeys]: AllowedValue
}
type Config = ExtendsFrom<BaseConfig, {
blah: string,
blah2: boolean,
}>
sindresorhus / type-fest
A collection of essential TypeScript types
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