type assertion

@nick/is/type/assertion

Assertion

Signature

export type Assertion<
  Type extends Base = any,
  Base = unknown,
  Args extends readonly unknown[] = readonly any[],
> = Expand<(it: Base, ...args: Args) => asserts it is Type>;

Represents an assertion function that checks if a given value of the base type Base is also of the derived type Type. If the value is not of the derived type, it will throw an error.

Type Parameters

• Type extends Base (default: any)
• Base (default: unknown)
• Args extends readonly unknown[] (default: readonly any[])

---

Examples

const assertString: Assertion<string> = (it: unknown): asserts it is string => {
  if (typeof it !== "string") {
    throw new TypeError("Expected a string");
  }
};