Why can't I pass `Omit<MyUnion, 'one key'>` into a function that requires `MyUnion`?

[bitter sphinx]

bawdyinkslinger#0

Playground Link

Preview:ts export type WaitStrategy = ( debugNote?: string, timeoutMillis?: number ) => Promise<void> declare const waitForPassageEnd: WaitStrategy declare const waitForClickEnd: WaitStrategy export type WaitStrategyType = | ":passageend" | "click end" | WaitStrategy ...

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[trim sequoia]

!ts

[bitter sphinx]

export type WaitStrategy = (
  debugNote?: string,
  timeoutMillis?: number,
) => Promise<void>;
declare const waitForPassageEnd: WaitStrategy;
declare const waitForClickEnd: WaitStrategy;
export type WaitStrategyType = ":passageend" | "click end" | WaitStrategy;

export const buildWaitStrategy = (
  waitStrategyType: WaitStrategyType,
): WaitStrategy => {
  switch (waitStrategyType) {
    case ":passageend":
      return waitForPassageEnd;
    case "click end":
      return waitForClickEnd;
    default:
      return waitStrategyType;
  }
};

declare const parameter: Omit<WaitStrategyType, "click end">;
buildWaitStrategy(parameter);
//                ^^^^^^^^^
// Argument of type 'Omit<WaitStrategyType, "click end">' is not assignable to parameter of type 'WaitStrategyType'.

[trim sequoia]

I can't think of a reason why this shouldn't be allowed, but I think I'm blinded by my specific use case. Can someone explain why this is worth preventing?

I get the same error if I add a elements:

[bitter sphinx]

bawdyinkslinger#0

Playground Link

Preview:ts export type WaitStrategy = ( debugNote?: string, timeoutMillis?: number ) => Promise<void> declare const waitForPassageEnd: WaitStrategy declare const waitForClickEnd: WaitStrategy export type WaitStrategyType = | ":passageend" | "click end" | WaitStrategy ...

You can choose specific lines to embed by selecting them before copying the link.

[trim sequoia]

!ts

[bitter sphinx]

export type WaitStrategy = (
  debugNote?: string,
  timeoutMillis?: number,
) => Promise<void>;
declare const waitForPassageEnd: WaitStrategy;
declare const waitForClickEnd: WaitStrategy;
export type WaitStrategyType = ":passageend" | "click end" | WaitStrategy;

export const buildWaitStrategy = (
  waitStrategyType: WaitStrategyType,
): WaitStrategy => {
  switch (waitStrategyType) {
    case ":passageend":
      return waitForPassageEnd;
    case "click end":
      return waitForClickEnd;
    default:
      return waitStrategyType;
  }
};

declare const parameter: ":passageend" | "click end" | WaitStrategy | "A new one";
buildWaitStrategy(parameter);
//                ^^^^^^^^^
// Argument of type 'WaitStrategy | ":passageend" | "click end" | "A new one"' is not assignable to parameter of type 'WaitStrategyType'.
//   Type '"A new one"' is not assignable to type 'WaitStrategyType'.

[serene ravine]

Omit is for objects, you want Exclude

[trim sequoia]

That fixed it, thanks

I feel like this documentation is confusing: https://www.typescriptlang.org/docs/handbook/utility-types.html#omittype-keys

The term "Type" is to general