is (function)

Returns whether value is of type type. Useful for validating that values have the correct type at runtime, in library functions or etc.

The type parameter can be any of the following:

• a TypeValidator function from the types namespace
• a global constructor like String, Number, Boolean, Set, Int8Array, etc
• a user-defined class
• a primitive value like true, false, null, or 42
• a Regular Expression (to match strings that match the regexp)
• an object or array containing any combination of the above

Note that yavascript has the following global aliases defined, which are also valid types:

const bigint = BigInt;
const boolean = Boolean;
const number = Number;
const string = String;
const symbol = Symbol;

Example

is(42, Number); // true
is(42, number); // true
is(42, types.number); // true

is(42, String); // false
is(42, Set); // false
is(42, Array); // false

is(42, 42); // true
is(42, 45); // false

is({ kind: "success", data: 99 }, { kind: "success" }); // true

// Defined in yavascript/src/api/is
declare function is(value: any, type: TypeValidator<any>): boolean;

See also types (which contains TypeValidators that can be used by is) and assert.type (which throws an error instead of returning a boolean).

const is: <T extends TypeValidator<any> | CoerceableToTypeValidator>(
  value: any,
  type: T,
) => value is UnwrapTypeFromCoerceableOrValidator<T>;

_is (value)

Alias to is, for when using the Civet language, because is is a reserved keyword in Civet.

const _is: typeof is;