@bitty/predicate

Predicate and Refinement types for TypeScript.

• 🏷 Safe:
  • JSDocs and type declarations for IDEs and editor's autocomplete/intellisense.
  • Made with TypeScript as strict as possible.
  • Unit tests with AVA.

Installation

This library is published in the NPM registry and can be installed using any compatible package manager.

npm install @bitty/predicate --save

# For Yarn, use the command below.
yarn add @bitty/predicate

Getting Stated

It exports Predicate and Refinement types.

• Predicate is a function that receives a value and returns a boolean.

  import type { Predicate } from '@bitty/predicate';
  
  function checkAll<T = unknown>(predicates: Predicate<T>[]): Predicate<T> {
    return (value) => predicates.every((predicate) => predicate(value));
  }

• Refinement is similar to Predicate, but uses TypeScript is type guard.

  import { Refinement } from '@bitty/predicate';
  
  const isNumber: Refinement<unknown, number> = (value) =>
    Number.isFinite(value);
  //=> Was typed as `(value: unknown) => value is number`.
  
  const value: number | string = Math.random() > 0.5 ? 100 : 'A text.';
  
  if (isNumber(value)) {
    console.log(value.toFixed(2));
    //=> Okay, because type of `value` was refined to `number`.
  }
  console.log(value.toFixed(2));
  //=> Property 'toFixed' does not exist on type 'string | number'.
  //     Property 'toFixed' does not exist on type 'string'.

License

Released under MIT License.