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assert (function)

const assert: {
  <ValueType>(
    value: ValueType,
    message?: string,
  ): asserts value is ValueType extends null | undefined | false | 0 | ""
    ? never
    : ValueType;
  type: <T extends TypeValidator<any> | CoerceableToTypeValidator>(
    value: any,
    type: T,
    optionalMessage?: string,
  ) => asserts value is UnwrapTypeFromCoerceableOrValidator<T>;
};

assert(...) (call signature)

Throws an error if value is not truthy.

  • @param value — The value to test for truthiness
  • @param message — An optional error message to use. If unspecified, "Assertion failed" will be used.
<ValueType>(value: ValueType, message?: string): asserts value is ValueType extends null | undefined | false | 0 | "" ? never : ValueType;

assert.type (function property)

Throws an error if its argument isn't the correct type.

  • @param value — The value to test the type of
  • @param type — The type that value should be, as either a TypeValidator (from the types.* namespace) or a value which can be coerced into a TypeValidator via the types.coerce function, like String, Boolean, etc.
  • @param message — An optional error message to use. If unspecified, a generic-but-descriptive message will be used.
type: <T extends TypeValidator<any> | CoerceableToTypeValidator>(value: any, type: T, optionalMessage?: string) => asserts value is UnwrapTypeFromCoerceableOrValidator<T>;