API reference › @evolu/common › Assert › assert

const assert: (
  condition: unknown,
  message: string,
  options?: {
    actual?: unknown;
    cause?: unknown;
    diff?: "full";
    expected?: unknown;
    operator?: string;
    stackStartFn?: (...args: never[]) => unknown;
  },
) => asserts condition;

Defined in: packages/common/src/Assert.ts:88

Asserts that a condition is truthy.

Throws an AssertionError with the provided message if the condition is falsy, preventing invalid state from propagating and making the failure easier to diagnose.

Use assert only when a more specific assertion, such as assertTrue or assertEqual, does not apply. For that reason, assert requires a custom message explaining the expected condition.

Options provide structured diagnostics for custom assertions. Pass an underlying failure as cause when it explains why the asserted condition failed, and pass the custom assertion as stackStartFn to omit its implementation from the stack trace.

Example

import { assert, assertEqual, assertType } from "@evolu/common";

const value: unknown = "Evolu";
assert(typeof value === "string", "Expected a string.");

assertType<typeof value, string>();
assertEqual(value, "Evolu");