I want to define a generic type ExcludeCart<T> that is essentially T but with a given key (in my case, cart) removed. So, for instance, ExcludeCart<{foo: number, bar: string, cart: number}> would be {foo: number, bar: string}. Is there a way to do this in TypeScript?
Here's why I want to do this, in case I'm barking up the wrong tree: I'm converting an existing JavaScript codebase to TypeScript, which contains a decorator function called cartify that takes a React component class Inner and returns another component class Wrapper.
Inner should take a cart prop, and zero or more other props. Wrapper accepts a cartClient prop (which is used to generate the cart prop to pass to Inner), and any prop that Inner accepts, except cart.
In other words, once I can figure out how to define ExcludeCart, I want to do this with it:
function cartify<P extends {cart: any}>(Inner: ComponentClass<P>) : ComponentClass<ExcludeCart<P> & {cartClient: any}>
Update for TypeScript 3.5: The Omit<Type, Keys> utility type is now available. Please see Mathias' answer for an example usage.
Old Answer: Since TypeScript 2.8 and the introduction of Exclude, It's now possible to write this as follows:
type Without<T, K> = {
[L in Exclude<keyof T, K>]: T[L]
};
Or alternatively, and more concisely, as:
type Without<T, K> = Pick<T, Exclude<keyof T, K>>;
For your usage, you could now write the following:
type ExcludeCart<T> = Without<T, "cart">;
While this has been correctly answered, I wanted to point out that TypeScript 3.5 did add an Omit<T, E> type.
type NoCart = Omit<{foo: string, bar: string, cart: number}, "cart">;
This results in the {foo: string, bar: string} type.
While there isn't a built-in subtraction type, you can currently hack it in:
type Sub0<
O extends string,
D extends string,
> = {[K in O]: (Record<D, never> & Record<string, K>)[K]}
type Sub<
O extends string,
D extends string,
// issue 16018
Foo extends Sub0<O, D> = Sub0<O, D>
> = Foo[O]
type Omit<
O,
D extends string,
// issue 16018
Foo extends Sub0<keyof O, D> = Sub0<keyof O, D>
> = Pick<O, Foo[keyof O]>
In the question's case, you would do:
type ExcludeCart<T> = Omit<T, 'cart'>
With TypeScript >= 2.6, you can simplify it to:
/**
* for literal unions
* @example Sub<'Y' | 'X', 'X'> // === 'Y'
*/
export type Sub<
O extends string,
D extends string
> = {[K in O]: (Record<D, never> & Record<string, K>)[K]}[O]
/**
* Remove the keys represented by the string union type D from the object type O.
*
* @example Omit<{a: number, b: string}, 'a'> // === {b: string}
* @example Omit<{a: number, b: string}, keyof {a: number}> // === {b: string}
*/
export type Omit<O, D extends string> = Pick<O, Sub<keyof O, D>>