ts-enum-util

Strictly typed utilities for working with TypeScript enums (and string/number literal union types).

NOTE: Be sure to read about supported TypeScript versions in the Requirements section.

Contents

• What is it?
  • Enum Wrapper Utilities
  • Enum Value Visitor/Mapper
• Installation
• Getting Started
• Usage Documentation/Examples
• Requirements
• Why is the main export named $enum?

What is it?

ts-enum-util provides type-safe utilities to improve the usefulness of TypeScript enums. There are two major and distinct aspects to ts-enum-util.

Enum Wrapper Utilities

A wrapper around an enum, or "enum-like object", that provides a variety of type-safe utilities in terms of the run-time representation fo the enum's keys/values. Some examples include:

• Get a list of an enum's keys, values, or key/value pairs.
• Look up values by key with run-time key validation and optional result defaulting.
• Reverse lookup of keys by value (for string enums too!) with run-time value validation and optional result defaulting.
• Run-time validation that a specified value or key is valid for a given enum, with compile-time type guards.
• Treat an enum similar to an Array of key/value tuples.
• Treat an enum similar to a Map of values.

All of these utilities are very specifically typed for each enum via generics and type inference.

Enum Value Visitor/Mapper

A visitor pattern for processing a single value whose type is an enum, or union of string/number literals. It's like a switch statement that forces you to implement every possible case (including null or undefined, if relevant), avoiding bugs because you forgot to handle one of the enum's values, or because the enum definition was updated with a new value and you forgot to update existing code to handle the new value.

The more generalized "visit" functionallity has you associate a different function with each possible value of an enum or string/number literal union. The appropriate function is executed (and its return value returned) based on which value the argument is at run-time.

A streamlined "map" functionality has you simply associate values (of any type) with each possible value of an enum or string/number literal union. The appropriate mapped value is returned based on which value the argument is at run-time.

Installation

Install via NPM:

npm i -s ts-enum-util

Getting Started

Import $enum:

import { $enum } from "ts-enum-util";

Define an enum:

enum Color {
    R,
    G,
    B
}

Use $enum() as a function to access Enum Wrapper Utilities for your enum:

// type of "values": Color[]
// value of "values": [0, 1, 2]
const values = $enum(Color).getValues();

Use $enum.visitValue() or $enum.mapValue() to access Enum Value Visitor/Mapper functionality:

function doColorAction(color: Color): void {
    $enum.visitValue(color).with({
        [Color.R]: () => {
            window.alert("Red Alert!");
        },
        [Color.G]: () => {
            window.location = "http://google.com";
        },
        [Color.B]: () => {
            console.log("Blue");
        }
    });
}

function getColorLabel(color: Color | undefined): string {
    return $enum.mapValue(color).with({
        [Color.R]: "Red",
        [Color.G]: "Green",
        [Color.B]: "Blue",
        [$enum.handleUndefined]: "Unspecified"
    });
}

Usage Documentation/Examples

To keep the size of the README under control, usage documentation and examples have been split out to separate files:

• Enum Wrapper Utilities
• Enum Value Visitor/Mapper
  • Migration Guide: from ts-string-visitor

Requirements

• TypeScript 2.9+: ts-enum-util is all about strictly type-safe utilities around TypeScript enums, so it would be much less useful in a plain JavaScript project. More specifically, TypeScript 2.9 included advancements in handling number literals as property names of object types, which is necessary for implementing some ts-enum-util functionality consistently for both string and number enum types.
  • Stuck with an older version of TypeScript?
    • For Value Visitor/Mapper functionality, check out ts-string-visitor (npm, github). NOTE: numeric value visiting/mapping not supported!
    • For Enum Wrapper functionality, check out v3 or v2 of ts-enum-util.
• ES6 Features: The following ES6 features are used by ts-enum-util, so they must exist (either natively or via polyfill) in the run-time environment:
  • Map
  • WeakMap
  • Symbol
  • Symbol.iterator
  • Symbol.toStringTag

Why is the main export named $enum?

I wanted something short, simple, and easy to remember that was unlikely to conflict with anything else so that no one would have to alias it when importing it. By exporting a clear, memorable, and uniquely named "thing", this allows you to simply start writing code that uses $enum and most IDEs can take care of inserting the import { $enum } from "ts-enum-util"; for you (either automatically, or with a quick keyboard shortcut).

I ended up using inspiration from the naming of jquery's $() function. Many javascript developers are familiar with jquery, and the fact that $() gives you a wrapper around a raw DOM element to expose additional/simplified functionality around the DOM element.

Similarly, $enum() gives you a wrapper around a raw enum to expose additional/simplified functionality around the enum.