awslabs/llrt · error · TypeError

value must be , received

Error message

${name} value must be ${types.join(" or ")}, received "${receivedType}"

What it means

This TypeError is thrown by the `assertTypes` helper in @llrt/expect, used by matchers to validate that the expectation value has one of the allowed JavaScript types. It computes `typeof value` and compares against the accepted type list; on mismatch it reports the expected types joined by 'or' and the actual received type. JestChaiExpect matchers call it before performing comparisons.

Solutions

Convert the value to the expected type before asserting (Number('1.5'), etc.).
Check the value with typeof / an if-guard before the matcher call.
Fix the source of the value so it produces the intended type (often an API returned null).

Example fix

// before
expect(result.rate).toBeCloseTo(0.5); // result.rate is '0.5' (string)
// after
expect(Number(result.rate)).toBeCloseTo(0.5);

Defensive patterns

Strategy: validation

Validate before calling

if (typeof value !== 'number') throw new TypeError('toBeCloseTo expects a number, got ' + typeof value);

Type guard

function isType(v, ...types) {
  return types.includes(typeof v);
}

Prevention

Coerce values at the boundary (Number(), String()) before asserting.
Check for null/undefined from API responses before matching.
Update tests when the shape of returned data changes.

When it happens

Trigger: Calling a matcher that internally asserts types, e.g. expect(x).toBeCloseTo(nonNumber) or expect(x).toMatchObject(nonObject) — any call where the runtime typeof of the value is not in the matcher's allowed types array.

Common situations: Passing null/undefined where a primitive is expected, passing a string number ('1.5') to toBeCloseTo, or refactors that changed a value's type without updating the test.

Understand the failure class

Background: Type mismatch errors: IllegalArgumentException, TypeError and type guards across 150 open-source libraries — this error's family across 150 libraries.

Related errors

AI-assisted analysis of awslabs/llrt@742fc00b82 (2026-09-12). Data as JSON: /api/errors/7ebb07abf1322e35. Report an issue: GitHub.

Appendix: source

Thrown at llrt_core/src/modules/js/@llrt/expect/jest-expect.ts:634

            return recordAsyncExpect(test, promise);
          };
        },
      });

      return proxy;
    }
  );
};

export function assertTypes(
  value: unknown,
  name: string,
  types: string[]
): void {
  const receivedType = typeof value;
  const pass = types.includes(receivedType);
  if (!pass)
    throw new TypeError(
      `${name} value must be ${types.join(" or ")}, received "${receivedType}"`
    );
}

export function recordAsyncExpect(
  test: any,
  promise: Promise<any> | PromiseLike<any>
) {
  // record promise for test, that resolves before test ends
  if (test && promise instanceof Promise) {
    // if promise is explicitly awaited, remove it from the list
    promise = promise.finally(() => {
      const index = test.promises.indexOf(promise);
      if (index !== -1) test.promises.splice(index, 1);
    });

    // record promise
    if (!test.promises) test.promises = [];

View on GitHub (pinned to 742fc00b82)