sindresorhus/is · error · TypeError

Expected value which is `BigInt64Array`, received value of t

Error message

Expected value which is `BigInt64Array`, received value of type `${is(value)}`.

What it means

Thrown by `assertBigInt64Array(value)` when the value's object tag is not `BigInt64Array`. Only a genuine `BigInt64Array` passes — a `BigUint64Array`, a `Float64Array`/`Int32Array`, a plain array of bigints, an `ArrayBuffer`, or a `DataView` over the same bytes all fail even though they may hold equivalent data.

Source

Thrown at source/index.ts:1492

		throw new TypeError(message ?? typeErrorMessage('AsyncGeneratorFunction', value));
	}
}

export function assertAsyncIterable<T = unknown>(value: unknown, message?: string): asserts value is AsyncIterable<T> {
	if (!isAsyncIterable(value)) {
		throw new TypeError(message ?? typeErrorMessage('AsyncIterable', value));
	}
}

export function assertBigint(value: unknown, message?: string): asserts value is bigint {
	if (!isBigint(value)) {
		throw new TypeError(message ?? typeErrorMessage('bigint', value));
	}
}

export function assertBigInt64Array(value: unknown, message?: string): asserts value is BigInt64Array {
	if (!isBigInt64Array(value)) {
		throw new TypeError(message ?? typeErrorMessage('BigInt64Array', value));
	}
}

export function assertBigUint64Array(value: unknown, message?: string): asserts value is BigUint64Array {
	if (!isBigUint64Array(value)) {
		throw new TypeError(message ?? typeErrorMessage('BigUint64Array', value));
	}
}

export function assertBlob(value: unknown, message?: string): asserts value is Blob {
	if (!isBlob(value)) {
		throw new TypeError(message ?? typeErrorMessage('Blob', value));
	}
}

export function assertBoolean(value: unknown, message?: string): asserts value is boolean {
	if (!isBoolean(value)) {
		throw new TypeError(message ?? typeErrorMessage('boolean', value));

View on GitHub ↗ (pinned to 7821031c66)

Solutions

Construct the proper view: `new BigInt64Array(arrayOfBigints)` or `new BigInt64Array(buffer, byteOffset, length)` — the byte length must be a multiple of 8.
If you have a BigUint64Array and the signed type is required, create a signed view over the same buffer: `new BigInt64Array(u.buffer, u.byteOffset, u.length)` (mind reinterpretation of values ≥ 2^63).
If any 64-bit bigint view is acceptable, assert `assert.any([is.bigInt64Array, is.bigUint64Array], value)`.
Verify the runtime supports BigInt64Array (Node 10.4+/modern browsers) rather than a fallback shim.

Example fix

// before
assert.bigInt64Array([1n, 2n]); // plain Array, throws
// after
assert.bigInt64Array(new BigInt64Array([1n, 2n]));

Defensive patterns

Strategy: type-guard

Validate before calling

if (!(value instanceof BigInt64Array)) {
  // e.g. construct: new BigInt64Array(buffer) — do not pass the raw buffer
}

Type guard

const isBigInt64Array = (value) => value instanceof BigInt64Array;

Try / catch

try {
  assert.bigInt64Array(value);
} catch (error) {
  if (error instanceof TypeError) { /* wrong TypedArray flavor or raw ArrayBuffer */ }
  else { throw error; }
}

Prevention

BigUint64Array, Int32Array, and raw ArrayBuffers all fail — the exact TypedArray class matters
Wrap buffers explicitly with new BigInt64Array(buffer, byteOffset, length) before passing
Cross-realm instances fail instanceof — prefer the library's is.bigInt64Array guard for values crossing realms/workers

When it happens

Trigger: Passing an ordinary array like `[1n, 2n]` instead of `new BigInt64Array([1n, 2n])`; passing the unsigned variant `BigUint64Array` where the signed one is asserted; passing a raw `ArrayBuffer`/`Buffer` from I/O without wrapping it in the correct view; a `Number`-based typed array used for 64-bit values that actually need bigint precision.

Common situations: WebAssembly/FFI or binary-protocol code where buffers arrive as Node `Buffer`/`ArrayBuffer` and need an explicit `new BigInt64Array(buf.buffer, ...)` view; sign confusion between Int64/Uint64 columns; environments predating BigInt64Array (Safari < 15, old Node) where a polyfill or fallback array is substituted.

Related errors

AI-assisted analysis of sindresorhus/is@7821031c66 (2026-07-31). Data as JSON: /data/errors/154087aeaf585d7f.json. Report an issue: GitHub ↗.