Module index

Runtime/value type guards, safe casts, deep equality and immutability, error utilities.

Runtime Guards

Type guards for runtime JavaScript types and protocols.

import { isDefined, isEmpty, isFunction, isPromise, isIterable } from '@metreeca/core';

if (isDefined<T>(value)) {
  // value is T
}
and define T

isEmpty({}); // true
isEmpty([]); // true

isFunction(() => {}); // true
isPromise(Promise.resolve(42)); // true
isIterable([1, 2, 3]); // true

isDefined: Checks if a value is not undefined or null.
isEmpty: Checks if a value is an empty plain object or an empty array.
isSymbol: Checks if a value is a symbol.
isFunction: Checks if a value is a function.
isError: Checks if a value is an Error instance.
isPromise: Checks if a value is a promise.
isIterable: Checks if a value is iterable.
isAsyncIterable: Checks if a value is async iterable.

Value Guards

Type guards for JSON-like values and data structures.

import { isBoolean, isNumber, isString, isObject, isArray } from '@metreeca/core';

isBoolean(true); // true
isNumber(42); // true (excludes NaN, Infinity)
isString('hello'); // true

isObject({ a: 1 }); // true
isObject(new Date()); // false

isArray([1, 2, 3], isNumber); // true
isArray([1, 'two'], isNumber); // false

isBoolean: Checks if a value is a boolean.
isNumber: Checks if a value is a finite number.
isString: Checks if a value is a string.
isObject: Checks if a value is a plain object.
isArray: Checks if a value is an array.

Value Casts

Safe casts for JSON-like primitive values and data structures, returning undefined instead of throwing.

import { asNumber, asString, asObject, asArray } from '@metreeca/core';

asNumber(42); // 42
asNumber('42'); // undefined

asBoolean: Retrieves a value as a boolean if it is one, otherwise returns undefined.
asNumber: Retrieves a value as a number if it is one, otherwise returns undefined.
asString: Retrieves a value as a string if it is one, otherwise returns undefined.
asObject: Retrieves a value as a plain object if it is one, otherwise returns undefined.
asArray: Retrieves a value as an array if it is one, otherwise returns undefined.

Structural Utilities

Deep operations on complex types.

import { equals, immutable } from '@metreeca/core';

equals({ a: [1, 2] }, { a: [1, 2] }); // true
immutable({ a: [1, 2, 3] }); // deep frozen

equals: Checks deep object equality.
immutable: Creates an immutable deep clone.