Type Alias IsEqual<A, B>

IsEqual: <G>() => G extends A ? 1 : 2 extends <G>() => G extends B ? 1 : 2
    ? true
    : false

Returns a boolean for whether the two given types are equal.

Type Parameters

  • A
  • B

Link

https://github.com/microsoft/TypeScript/issues/27024#issuecomment-421529650

Link

https://stackoverflow.com/questions/68961864/how-does-the-equals-work-in-typescript/68963796#68963796

Use-cases:

  • If you want to make a conditional branch based on the result of a comparison of two types.

Example

import type {IsEqual} from 'type-fest';

// This type returns a boolean for whether the given array includes the given item.
// `IsEqual` is used to compare the given array at position 0 and the given item and then return true if they are equal.
type Includes<Value extends readonly any[], Item> =
	Value extends readonly [Value[0], ...infer rest]
		? IsEqual<Value[0], Item> extends true
			? true
			: Includes<rest, Item>
		: false;

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