Package Exports

isguard-ts
isguard-ts/dist/index.js

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Readme

isguard-ts

A powerful typescript library that helps you build type guards.
isguard-ts utilizes the typescript compiler to ensure the type guards are type safe and fast to create.

Some of our built-in helper functions

isType
isTuple
isUnion
isIntersection
isArray
isEnum
isSet
isMap
isRecord
isIndexRecord
isInstanceof
isOptional
isMaybe

Some of our utility type guards

isString
isStringArray
isNumber
isDate
isNull
isUndefined
isNil - null or undefined
isUnknown - always returns true
isNever - always returns false

Code Examples

`TypeGuard<T>`

The most basic type - represents a type guard of T

type TypeGuard<T> = (value: unknown) => value is T;

`Guarded<T>`

Extracts T out of TypeGuard<T>

type Test = Guarded<TypeGuard<number>>; // number

`isType<T>(template): TypeGuard<T>`

Helps you create type guards for types and interfaces

type Person = {
    name: string;
    age: number;
};

const isPerson = isType<Person>({
    name: isString,
    age: isNumber,
});

isPerson({ name: "Hello", age: 6 }) // true

isType also supports recursive types by passing a function as an argument

type Tree = {
    value: number;
    left: Tree | null;
    right: Tree | null;
};

const isTree = isType<Tree>(() => ({
    value: isNumber,
    left: isMaybe(isTree), // isTree is the return type of isType
    right: isMaybe(isTree),
}));

// isTree can also be accessed via the passed function's parameter
const isTree2 = isType<Tree>(isTreeParam => ({
    value: isNumber,
    left: isMaybe(isTreeParam), // isTreeParam === isTree2
    right: isMaybe(isTreeParam),
}));

For generic types you would need to create your own type guard generator

type ValueHolder<T> = {
    value: T;
};

const isValueHolder = <T>(isValue: TypeGuard<T>): TypeGuard<ValueHolder<T>> => {
    return isType<ValueHolder<T>>({
        value: isValue,
    });
};

const isNumberHolder: TypeGuard<ValueHolder<number>> = isValueHolder(isNumber);

`isTuple<T>(template): TypeGuard<T>`

Helps you create type guards for tuples

type Row = [number, string?];

const isRow = isTuple<Row>([isNumber, isOptionalString]);

isRow([6, "Hello"]) // true
isRow([6]) // true
isRow(["Hello", "Bye"]) // false

Just like isType, isTuple supports recursive tuples

type Row = [number, Row | null];

const isRow = isTuple<Row>(() => [
    isNumber,
    isMaybe(isRow),
]);

// isRow can also be accessed via the function's parameter
const isRow = isTuple<Row>(isRowParam => [
    isNumber,
    isMaybe(isRowParam), // isRowParam === isRow2
]);

`isUnion<[T1, T2, ...]>(...guards): TypeGuard<T1 | T2 | ...>`

Helps you create type guards for unions

const isNumberOrString: TypeGuard<number | string> = isUnion(isNumber, isString);

isNumberOrString(6) // true
isNumberOrString("Hello") // true
isNumberOrString(new Date()) // false

`isIntersection<[T1, T2, ...]>(...guards): TypeGuard<T1 & T2 & ...>`

Helps you create type guards for intersections

type A = { a: number };
type B = { b: string };
type C = A & B;

const isA = isType<A>({ a: isNumber });
const isB = isType<B>({ b: isString });

const isC: TypeGuard<C> = isIntersection(isA, isB);

`isArray<T>(guard: TypeGuard<T>): TypeGuard<T[]>`

Helps you create type guards for arrays

const isNumberArray = isArray(isNumber);

type Test = { a: number };
const isTest = isType<Test>({ a: isNumber });
const isTestArray: TypeGuard<Test[]> = isArray(isTest);

`isEnum<T>(enumObj: T): TypeGuard<T[keyof T]>`

Helps you create type guards for enums

enum Direction {
    up = 0,
    down = 1,
    left = 2,
    right = 3,
}

const isDirection: TypeGuard<Direction> = isEnum(Direction);
isDirection(Direction.up) // true
isDirection(2) // true
isDirection("hello") // false

`isSet<T>(guard: TypeGuard<T>): TypeGuard<Set<T>>`

Helps you create type guards for sets

const isNumberSet = isSet(isNumber);

`isMap<K, V>(isKey: TypeGuard<K>, isValue: TypeGuard<V>): TypeGuard<Map<K, V>>`

Helps you create type guards for maps

const isStringBooleanMap = isMap(isString, isBoolean);

`isRecord<K, V>(isKey: TypeGuard<K>, isValue: TypeGuard<V>): TypeGuard<Record<K, V>>`

Helps you create type guards for records

type TimeUnit = "second" | "minute" | "hour";
type TimeUnitToMillisecond = Record<TimeUnit, number>;

const isTimeUnit: TypeGuard<TimeUnit> = isValueUnion("second", "minute", "hour");
const isTimeUnitToMillisecond = isRecord(isTimeUnit, isNumber);

`isIndexRecord<V>(isValue: TypeGuard<V>): TypeGuard<Record<PropertyKey, V>>`

Works just like isRecord but checks only the values and not the keys

const isNumberRecord: TypeGuard<Record<PropertyKey, number>> = isIndexRecord(isNumber);

`isInstanceof<T>(constructor): TypeGuard<T>`

Helps you create type guards for classes

abstract class Animal { }
class Dog extends Animal { }

const isAnimal: TypeGuard<Animal> = isInstanceof(Animal);
const isDog: TypeGuard<Dog> = isInstanceof(Dog);

`isOptional<T>(guard: TypeGuard<T>): TypeGuard<T | undefined>`

Helps you create type guards for optional types

const isNumberOrUndefined: TypeGuard<number | undefined> = isOptional(isNumber);

`isMaybe<T>(guard: TypeGuard<T>): TypeGuard<T | null>`

Helps you create type guards for nullable types

const isNumberOrNull: TypeGuard<number | null> = isMaybe(isNumber);