iansan5653 / improved-record

Leverages the abilities of the TypeScript compiler to improve immutable.js' Record.

Improved Immutable Record

ImprovedRecord is a lightweight wrapper around the immutable.js Record type. This is intended only for use with TypeScript, as it takes advantage of the type system to ensure safety while allowing for more flexible use.

The primary benefit of ImprovedRecord is the ability to declare properties that do not have a default value. These properties are required to be set when creating a new record instance, and they cannot be deleted (only changed).

ImprovedRecord is inspired by Scala's case classes, which work in a very similar way.

Comparison with immutable.js Record

	immutable.js Record	ImprovedRecord
Properties can be declared without defaults	❌	✅
Properties can be deleted (reset to default)	✅	Only properties with defaults
Shape easily defined by TypeScript interfaces	✅	✅
100% safe at runtime	✅	❌
100% safe at compile-time	✅	✅
Completely immutable	✅	✅

Getting Started

Installation

NPM

npm i improved-record

Yarn

yarn add improved-record

Usage

The API for ImprovedRecord is almost exactly the same as the API for the original Record.

Here are all the differences:

• The shape interface type parameter is required (cannot be correctly inferred).
• When creating factories, default values can only be specified for optional properties on the shape interface (properties defined like property?: Type).
• When creating factories, all required properties must have their default set to the unique required symbol. This is required because of how immutable.js works behind the scenes.
• undefined cannot be used as a default value or as a value for required types. Use null instead.
• When creating record instances, all properties without default values (required properties in the shape interface) are required. Properties with default values can still be overridden.
• When calling delete or remove on an instance, only properties with defaults (optional properties in the shape interface) may be deleted. Names of properties without defaults cannot be passed.
• The clear method is not available (because there are no default values for some properties).
• The deleteIn and removeIn methods are not available (because there is no way to safely type- check these methods and prevent required properties from being deleted).

That's it! Everything else is the same.

Example

Here's a full example with a sample Person record:

Defining a factory

import {ImprovedRecord, ImprovedRecordOf, required} from "improved-record";

// The props interface is required (cannot be correctly inferred from the default values):
interface PersonProps {
  // For required properties like this, no default value will be defined.
  username: string;
  // Properties marked optional will always have a default value defined.
  level?: "admin" | "user";
  // The `| undefined` here will have no effect as `undefined` is not a valid value.
  displayName: string | undefined;
  // For truly optional properties, `null` can be used as the default value. `undefined` cannot be
  // the default value.
  age?: number | null;
}

// Now create the record factory. Providing the props interface is required.
const Person = ImprovedRecord<PersonProps>({
  // Set required properties to the unique `required` symbol.
  username: required,
  // Any optional property *must* have a default value.
  level: "user",
  // Even though `displayName` has `| undefined`, it is still a required property (no `?:`).
  displayName: required,
  age: null
});

// Define the record instance type with the same name as the record factory (this is optional but
// makes it much easier to work with and helps to avoid accidentally using `PersonProps` instead of
// `Person`.
type Person = ImprovedRecordOf<PersonProps>;

export default Person;

Using the factory

import Person from "Person";

// Using the factory method:
const samplePerson = Person({
  // Required properties must be defined.
  username: "sample123",
  // `displayName` cannot be set to `undefined`
  displayName: "unknown"
  // `age` and `level` don't have to be set because they have defaults.
});

// `Person` is also a type due to declaration merging:
const doSomething = (person: Person): void => {
  /* ... */
};

doSomething(samplePerson);