API reference › @evolu/common › Type › assertType

Call Signature

function assertType<Expected, Actual>(
  ...error: IsSameType<Expected, Actual> extends true
    ? []
    : ["⛔ assertType error: Expected and actual types must be identical"]
): void;

Defined in: packages/common/src/Type.ts:1073

Asserts exact compile-time type equality or that a value belongs to a Type Output domain.

  • assertType<Expected, Actual>() requires compiler-identical types without evaluating a value.
  • assertType(type, value) validates and narrows a runtime value to the Type's Output.

Use the runtime form for internal invariants, not external input. Validate external input with Type.fromUnknown so validation failures remain typed values. A failed runtime assertion uses the Type name for its message and preserves the exact Output validation error as the thrown Error's cause.

Example

import {
  NonEmptyTrimmedString100,
  assertType,
  type Brand,
} from "@evolu/common";

const value: unknown = "Evolu";
assertType(NonEmptyTrimmedString100, value);
assertType<
  string & Brand<"Trimmed"> & Brand<"MinLength1"> & Brand<"MaxLength100">,
  typeof value
>();

Call Signature

function assertType<T>(type: T, value: unknown): asserts value is T["Output"];

Defined in: packages/common/src/Type.ts:1083

Asserts exact compile-time type equality or that a value belongs to a Type Output domain.

  • assertType<Expected, Actual>() requires compiler-identical types without evaluating a value.
  • assertType(type, value) validates and narrows a runtime value to the Type's Output.

Use the runtime form for internal invariants, not external input. Validate external input with Type.fromUnknown so validation failures remain typed values. A failed runtime assertion uses the Type name for its message and preserves the exact Output validation error as the thrown Error's cause.

Example

import {
  NonEmptyTrimmedString100,
  assertType,
  type Brand,
} from "@evolu/common";

const value: unknown = "Evolu";
assertType(NonEmptyTrimmedString100, value);
assertType<
  string & Brand<"Trimmed"> & Brand<"MinLength1"> & Brand<"MaxLength100">,
  typeof value
>();
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