core.assertnever

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assertNever() function

Checks that a value has type never. Useful for ensuring exhaustive matches.

Signature:

export declare function assertNever(value: never): never;

Parameters

Parameter	Type	Description
value	never	The value that should never be present

Returns:

never

Example

  type MyUnion = 'a' | 'b' | 'c'
  function f(arg: MyUnion) {
    if (arg === 'a') { return 1; }
    if (arg === 'b') { return 2; }
    assertNever(arg); // Type error: 'c' is unhandled
  }