#assertSheet

Asserts that a value is a sheet, narrowing its type, and throws if it is not.

import { Sheet } from "@teakit/sheet";

const input: unknown = { "2024": [1, 2] };

Sheet.assertSheet(input);
// input is now typed as Sheet<unknown>; no clone is made.
Sheet.sum(input); // 3

Sheet.assertSheet([1, 2]); // throws SheetError "SHEET_INVALID_SHEET"

#API Reference

#Signature

Sheet.assertSheet(value: unknown): asserts value is Sheet<unknown>;

#Parameters

#Returns

void. Narrows value to Sheet<unknown> on success. Does not clone.

#Throws

• SHEET_INVALID_SHEET — value is not a valid sheet structure (same rule as from).

#Agent Contract

#Agent Notes

• Use assertSheet when an invalid value should be an error; use isSheet when you want a boolean branch.
• It validates only; to also get a key-ascending clone, use from.