Function assertInstanceOf

assert/instance_of.ts:28–64

(
  actual: unknown,
  expectedType: T,
  msg = "",
)

 * @param msg The optional message to display if the assertion fails.
 */
export function assertInstanceOf<
  // deno-lint-ignore no-explicit-any
  T extends abstract new (...args: any[]) => any,
>(
  actual: unknown,
  expectedType: T,
  msg = "",
): asserts actual is InstanceType<T> {
  if (actual instanceof expectedType) return;

  const msgSuffix = msg ? `: ${msg}` : ".";
  const expectedTypeStr = expectedType.name;

  let actualTypeStr = "";
  if (actual === null) {
    actualTypeStr = "null";
  } else if (actual === undefined) {
    actualTypeStr = "undefined";
  } else if (typeof actual === "object") {
    actualTypeStr = actual.constructor?.name ?? "Object";
  } else {
    actualTypeStr = typeof actual;
  }

  if (expectedTypeStr === actualTypeStr) {
    msg =
      `Expected object to be an instance of "${expectedTypeStr}"${msgSuffix}`;
  } else if (actualTypeStr === "function") {
    msg =
      `Expected object to be an instance of "${expectedTypeStr}" but was not an instanced object${msgSuffix}`;
  } else {
    msg =
      `Expected object to be an instance of "${expectedTypeStr}" but was "${actualTypeStr}"${msgSuffix}`;
  }

  throw new AssertionError(msg);
}