unknownutil

A utility pack for handling unknown type.

Install

Install via npm:

npm install --save unknownutil

Usage

It provides is module for type predicate functions and assert, ensure, and maybe helper functions.

is*

Type predicate function is a function which returns true if a given value is expected type. For example, isString (or is.String) returns true if a given value is string.

import { is } from "unknownutil";

const a: unknown = "Hello";
if (is.String(a)) {
  // 'a' is 'string' in this block
}

For more complex types, you can use is*Of (or is.*Of) functions like:

import { is, PredicateType } from "unknownutil";

const isArticle = is.ObjectOf({
  title: is.String,
  body: is.String,
  refs: is.ArrayOf(
    is.UnionOf([
      is.String,
      is.ObjectOf({
        name: is.String,
        url: is.String,
      }),
    ]),
  ),
  createTime: is.OptionalOf(is.InstanceOf(Date)),
  updateTime: is.OptionalOf(is.InstanceOf(Date)),
});

// Infer the type of `Article` from the definition of `isArticle`
type Article = PredicateType<typeof isArticle>;

const a: unknown = {
  title: "Awesome article",
  body: "This is an awesome article",
  refs: [{ name: "Deno", url: "https://deno.land/" }, "https://github.com"],
};
if (isArticle(a)) {
  // a is narrowed to the type of `isArticle`
  console.log(a.title);
  console.log(a.body);
  for (const ref of a.refs) {
    if (is.String(ref)) {
      console.log(ref);
    } else {
      console.log(ref.name);
      console.log(ref.url);
    }
  }
}

Additionally, you can manipulate the predicate function returned from isObjectOf with isPickOf, isOmitOf, isPartialOf, and isRequiredOf similar to TypeScript's Pick, Omit, Partial, Required utility types.

import { is } from "unknownutil";

const isArticle = is.ObjectOf({
  title: is.String,
  body: is.String,
  refs: is.ArrayOf(
    is.UnionOf([
      is.String,
      is.ObjectOf({
        name: is.String,
        url: is.String,
      }),
    ]),
  ),
  createTime: is.OptionalOf(is.InstanceOf(Date)),
  updateTime: is.OptionalOf(is.InstanceOf(Date)),
});

const isArticleCreateParams = is.PickOf(isArticle, ["title", "body", "refs"]);
// is equivalent to
//const isArticleCreateParams = is.ObjectOf({
//  title: is.String,
//  body: is.String,
//  refs: is.ArrayOf(
//    is.UnionOf([
//      is.String,
//      is.ObjectOf({
//        name: is.String,
//        url: is.String,
//      }),
//    ]),
//  ),
//});

const isArticleUpdateParams = is.OmitOf(isArticleCreateParams, ["title"]);
// is equivalent to
//const isArticleUpdateParams = is.ObjectOf({
//  body: is.String,
//  refs: is.ArrayOf(
//    is.UnionOf([
//      is.String,
//      is.ObjectOf({
//        name: is.String,
//        url: is.String,
//      }),
//    ]),
//  ),
//});

const isArticlePatchParams = is.PartialOf(isArticleUpdateParams);
// is equivalent to
//const isArticlePatchParams = is.ObjectOf({
//  body: is.OptionalOf(is.String),
//  refs: is.OptionalOf(is.ArrayOf(
//    is.UnionOf([
//      is.String,
//      is.ObjectOf({
//        name: is.String,
//        url: is.String,
//      }),
//    ]),
//  )),
//});

const isArticleAvailableParams = is.RequiredOf(isArticle);
// is equivalent to
//const isArticlePutParams = is.ObjectOf({
//  body: is.String,
//  refs: is.ArrayOf(
//    is.UnionOf([
//      is.String,
//      is.ObjectOf({
//        name: is.String,
//        url: is.String,
//      }),
//    ]),
//  ),
//  createTime: is.InstanceOf(Date),
//  updateTime: is.InstanceOf(Date),
//});

If you need an union type or an intersection type, use isUnionOf and isIntersectionOf like:

import { is } from "unknownutil";

const isFoo = is.ObjectOf({
  foo: is.String,
});

const isBar = is.ObjectOf({
  bar: is.String,
});

const isFooOrBar = is.UnionOf([isFoo, isBar]);
// { foo: string } | { bar: string }

const isFooAndBar = is.IntersectionOf([isFoo, isBar]);
// { foo: string } & { bar: string }

assert

The assert function does nothing if a given value is expected type. Otherwise, it throws an AssertError exception like:

import { assert, is } from "unknownutil";

const a: unknown = "Hello";

// `assert` does nothing or throws an `AssertError`
assert(a, is.String);
// a is now narrowed to string

// With custom message
assert(a, is.String, { message: "a must be a string" });

ensure

The ensure function return the value as-is if a given value is expected type. Otherwise, it throws an AssertError exception like:

import { ensure, is } from "unknownutil";

const a: unknown = "Hello";

// `ensure` returns `string` or throws an `AssertError`
const _: string = ensure(a, is.String);

// With custom message
const __: string = ensure(a, is.String, { message: "a must be a string" });

maybe

The maybe function return the value as-is if a given value is expected type. Otherwise, it returns undefined that suites with nullish coalescing operator (??) like:

import { is, maybe } from "unknownutil";

const a: unknown = "Hello";

// `maybe` returns `string | undefined` so it suites with `??`
const _: string = maybe(a, is.String) ?? "default value";

Migration

See GitHub Wiki for migration to v3 from v2 or v2 from v1.

License

The code follows MIT license written in LICENSE. Contributors need to agree that any modifications sent in this repository follow the license.