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ts-enum-util | Enum Wrapper Utilities

Usage documentation for the EnumWrapper portion of ts-enum-util.

Contents

Usage Examples

Here's several small examples ts-enum-util's Enum Wrapper capabilities to give you a quick overview of what it can do, as well as an organized "by example" reference.

Pay special attention to the comments indicating the compile-time type of various results. See Specific Typing for more about data types.

See API Reference for more details about method signatures and behaviors.

Basic setup for all examples

// import the $enum helper function
import { $enum } from "ts-enum-util";

// Example string enum
// (basic numeric enums also supported)
// (enums with a mix of numeric and string values also supported)
enum RGB {
    R = "r",
    G = "g",
    B = "b"
}

Get an EnumWrapper instance for an enum

Use the $enum function to get an EnumWrapper instance for a particular enum. Read about how EnumWrapper instances are cached: Caching.

// type: EnumWrapper<string, RGB>
const wrappedRgb = $enum(RGB);

Get count of enum entries

See also:

// Part of the Map-like interface implementation
// type: number
// value: 3
const size = $enum(RGB).size;

// Part of the Array-like interface implementation
// type: number
// value: 3
const length = $enum(RGB).length;

Get lists of enum data

See also:

// type: ("R" | "G" | "B")[]
// value: ["R", "G", "B"]
const keys = $enum(RGB).getKeys();

// type: RGB[]
// value: ["r", "g", "b"]
const values = $enum(RGB).getValues();

// List of key/value pair tuples
// type: [("R" | "G" | "B"), RGB][]
// value: [["R", "r"], ["G", "g"], ["B", "b"]]
const entries = $enum(RGB).getEntries();

Lookup value by key

// type: RGB
// value: "g"
const value1 = $enum(RGB).getValueOrThrow("G");

// throws: Error("Unexpected value: blah. Expected one of: R,G,B")
const value2 = $enum(RGB).getValueOrThrow("blah");

// type: RGB | undefined
// value: undefined
const value3 = $enum(RGB).getValueOrDefault("blah");

// type: RGB
// value: "r"
const value4 = $enum(RGB).getValueOrDefault("blah", RGB.R);

// type: string
// value: "BLAH!"
const value5 = $enum(RGB).getValueOrDefault("blah", "BLAH!");

Reverse lookup key by value

// type: ("R" | "G" | "B")
// value: "G"
const key1 = $enum(RGB).getKeyOrThrow("g");

// throws: Error("Unexpected value: blah. Expected one of: r,g,b")
const key2 = $enum(RGB).getKeyOrThrow("blah");

// type: ("R" | "G" | "B") | undefined
// value: undefined
const key3 = $enum(RGB).getKeyOrDefault("blah");

// type: ("R" | "G" | "B")
// value: "R"
const key4 = $enum(RGB).getKeyOrDefault("blah", "R");

// type: string
// value: "BLAH!"
const key4 = $enum(RGB).getKeyOrDefault("blah", "BLAH!");

Validate/convert enum keys

// Some arbitrary string
declare const str: string;

// Returns `true` if 'str' is a valid key of RGB
if ($enum(RGB).isKey(str)) {
    // isKey() is a type guard
    // type of 'str' in here is ("R" | "G" | "B")
}

// type: ("R" | "G" | "B")
// throws error if 'str' is not a valid key for RGB
const key1 = $enum(RGB).asKeyOrThrow(str);

// type: ("R" | "G" | "B") | undefined
// value is undefined if 'str' is not a valid key for RGB
const key2 = $enum(RGB).asKeyOrDefault(str);

// type: ("R" | "G" | "B")
// value is "G" if 'str' is not a valid key for RGB
const key3 = $enum(RGB).asKeyOrDefault(str, "G");

Validate/convert enum values

// Some arbitrary string
declare const str: string;

// Returns `true` if 'str' is a valid value of RGB
if ($enum(RGB).isValue(str)) {
    // isValue() is a type guard
    // type of 'str' in here is RGB
}

// type: RGB
// throws error if 'str' is not a valid value for RGB
const value1 = $enum(RGB).asValueOrThrow(str);

// type: RGB | undefined
// value is undefined if 'str' is not a valid value for RGB
const value2 = $enum(RGB).asValueOrDefault(str);

// type: RGB
// value is RGB.G if 'str' is not a valid value for RGB
const value3 = $enum(RGB).asValueOrDefault(str, RGB.G);

Iteration and Mapping

See also:

const wrappedRgb = $enum(RGB);

// iterate all entries in the enum
wrappedRgb.forEach((value, key, wrappedEnum, index) => {
    // type of value is RGB
    // type of key is ("R" | "G" | "B")
    // wrappedEnum is a reference to wrappedRgb
    // index is based on original defined order of the enum
});

// Convert all entries of the enum to an array of mapped values
// value: ["R: r", "G: g", "B: b"]
const mapped = wrappedRgb.map((value, key, wrappedEnum, index) => {
    // type of value is RGB
    // type of key is ("R" | "G" | "B")
    // wrappedEnum is a reference to wrappedRgb
    // index is based on original defined order of the enum
    return `${key}: ${value}`;
});

Wrapped enums are Array-Like

A wrapped enum is simialr to a readonly array of enum "entry" tuples.

See also:

const wrappedRgb = $enum(RGB);

// type: number
// value: 3
const length = wrappedRgb.length;

// type: [("R" | "G" | "B"), RGB]
// value: ["G", "g"]
const entry = wrappedRgb[1];

Wrapped enums are Map-Like

A wrapped enum is similar to a read-only Map of enum name -> enum value.

See also:

const wrappedRgb = $enum(RGB);

// type: number
// value: 3
const size = wrappedRgb.size;

// EnumWrapper is directly iterable like a Map
for (const [key, value] of wrappedRgb) {
    // type of key: ("R" | "G" | "B")
    // type of value: RGB
}

for (const key of wrappedRgb.keys()) {
    // type of key: ("R" | "G" | "B")
}

for (const value of wrappedRgb.values()) {
    // type of value: RGB
}

wrappedRgb.forEach((value, key, wrappedEnum, index) => {
    // type of value is RGB
    // type of key is ("R" | "G" | "B")
    // wrappedEnum is a reference to wrappedRgb
    // index is based on original defined order of the enum
    // NOTE: index param is extra compared to Map's forEach
});

Limitations

  • Does not work with enums that are merged with a namespace containing values (variables, functions, etc.), or otherwise have any additional properties added to the enum's runtime object.
  • Requires the preserveConstEnums TypeScript compiler option to work with const enums.
  • For certain Iterable features of WrappedEnum to work, you must either compile with a target of es6 or higher, or enable the downlevelIteration compiler option.

Known Issues

WeakMap Polyfill

WeakMap polyfills typically store values directly on the "key" object (the run-time enum object, in this case) as a non-enumerable "secret" (randomly generated) property. This allows for quick O(1) constant time lookups and garbage collection of the value along with the key object, but does add a property to the object. The WeakMap secret property will NOT be iterated in for ... in loops, and will NOT be included in the results of Object.keys(), but it WILL be included in the result of Object.getOwnPropertyNames().

It's hard to imagine this actually causing any problems, and all mainstream browsers have natively supported WeakMap since about 2014-2015, so I have decided to go ahead with relying on WeakMap. If you run into a problem caused by this, please report an issue on github.

Read more about the use of WeakMap for caching EnumWrapper instances here: Caching

General Concepts

Enum-Like Object

ts-enum-util technically works with any "enum-like" object, which is any object whose property values are of type string or number.

The most obvious example is a TypeScript enum. It can be a standard enum of numeric values, a string enum, or even an enum with a mix of numeric and string values.

EnumWrapper

The EnumWrapper class wraps around an enum-like object and implements all the useful utility methods for that enum.

You likely won't ever directly reference the EnumWrapper class because it's much more convenient to use the $enum() function to obtain a reference to an EnumWrapper instance.

Specific Typing

EnumWrapper is genericly typed based on the wrapped enum-like object with several method overloaded to ensure that params and results are as specifically-typed as possible.

For example, when obtaining a key or keys from an EnumWrapper, the data type will be a string literal union containing only the specific key names that exist in the enum.

This helps maximize the usefulness of EnumWrapper by making it compatible with other strictly typed code related to enums.

Map-Like Interface

A subset of EnumWrapper's interface overlaps with much of the ES6 Map interface. EnumWrapper is similar to a read-only Map of enum values, keyed by the enum names. The following Map-like features are implemented:

NOTE: The Map interface's has() and get() methods are intentionally NOT implemented in the interest of clarity and consistency of naming with respect to other EnumWrapper-specific methods. The equivalent methods are isKey and getValueOrDefault (with second param omitted).

Array-Like Interface

EnumWrapper implements the ArrayLike interface. It is usable as a readonly array of EnumWrapper.Entry. This allows you to pass an EnumWrapper instance to any method that is designed read/iterate an array-like value, such as most of lodash's methods for collections and arrays.

Order of Iteration

EnumWrapper does its best to retain the order in which the enum's entries were originally listed in source code.

When executed in an environment with an ES6-compliant implementation of Object.getOwnPropertyNames, then the order of iteration is guaranteed to match the order in which the enum was originally defined in source code.

If Object.getOwnPropertyNames is not available in the run-time environment, then there techincally is no official guarantee of the order in which the enum will be processed by EnumWrapper. However, a variety of de-facto standards of how various browsers and JS run-time environments have implemented object key/property ordering combined with limited subset of keys/properties processed by EnumUtil (own, enumerable, non-array-index properties only) allows for extremely high practical confidence that order of definition within the source code will be retained.

Example:

// enum defined with keys alphabetically out of order and
// values out of order
enum ABC = {
    B = 3,
    A = 1,
    C = 2
}

// defined order is retained: ["B", "A", "C"]
const values = $enum(ABC).getKeys();

// defined order is retained: [3, 1, 2]
const values = $enum(ABC).getValues();

Caching

EnumWrapper instances are cached using an ES6 WeakMap for quick subsequent retrieval via the $enum function. This allows you to easily access the EnumWrapper functionality for a given enum via the $enum function throughout your codebase without worrying about storing a reference to an EnumWrapper that is accessible by all of the relevant code.

The use of the WeakMap means that even if you use ts-enum-util on temporary, dynamically-generated, enum-like objects, there will be no excessive cache bloat or memory leaks. A cached EnumWrapper instance will be garbage collected when the enum-like object it is mapped to is garbage collected.

Although WeakMap lookups can be extremely efficient (constant time lookups in typical implementations), beware that the ECMAScript specification only requires lookups to be "on average" less than O(n) linear time. As such, you should still excercise caution against needlessly obtaining cached references via $enum when making heavy use of EnumWrapper functionality. Consider storing the result of $enum() in a local variable before making multiple calls to its methods, especially if the EnumWrapper's features are used within a loop.

Despite the above warning, it is noteworthy that even the worst case implementation still produces extremely quick lookups for a relatively small number of items (like the number of enums that you are likely have in a project). For example, see this performance test of lookups into maps containing 500 entries, including a simple Map polyfill implementation.

Read about a potential WeakMap Polyfill issue.

Read more about WeakMap on the MDN website.

API Reference

Also see the source code or the distributed .d.ts types files for complete details of method signatures/overloads, detailed method/param documentation, etc.

See Usage Examples if you prefer a "by example" reference.

Terminology

Throughout this reference, the following aliases for types will be used:

  • EnumLike: An enum-like object type. See Enum-Like Object.
  • KeyType: The type of the enum's keys. This is usually a string literal union type of the enum's names, but may also simply be string if an EnumWrapper was created for an object whose possible property names are not known at compile time.
  • EnumType: The specific enum type of the enum values. This is usually the enum type itself, but may also simply be the same as ValueType (see below) if a EnumWrapper was created for an object that is not actually an enum, but is only "enum-like".
  • ValueType: The widened type of the enum's values. Will be number, string, or number | string, depending on whether the wrapped enum-like object contains only number, only string, or both number and string values.

$enum

This is where it all begins. This method returns an EnumWrapper instance that provides useful utilities for enumObj.

See Caching for more about caching of EnumWrapper instances.

function $enum(enumObj: EnumLike): EnumWrapper;
  • enumObj - An enum or "enum-like" object.

Types

EnumWrapper

This is the class that implements all the enum utilities. It's a generic class that requires an overloaded helper function to properly instantiate, so the constructor is private. Use $enum() to get/create an instance of EnumWrapper.

class EnumWrapper

EnumWrapper.Entry

A generic type alias for a tuple containing a key and value pair, representing a complete "entry" in the enum. The tuple is defined as Readonly to prevent accidental corruption of the EnumWrapper instance's data.

type EnumWrapper.Entry = Readonly<[KeyType, EnumType]>

EnumWrapper.Iteratee

A generic type alias for a function signature to be used in iteration methods. This is compliant with the signature of an iteratee for a Map<KeyType, EnumType>.forEach() method, but also has an additional index param at the end of the parameter list.

See Order of Iteration for details about the ordering.

type EnumWrapper.Iteratee<R> = (
    value: EnumType,
    key: KeyType,
    enumWrapper: EnumWrapper,
    index: number
) => R
  • R - Generic type param for the return type of the function. The signifigance of the return type/value depends on teh context in which the iteratee is being used.
  • value - The value of the enum entry.
  • key - The key of the enum entry.
  • enumWrapper - A reference to the EnumWrapper instance that is being iterated.
  • index - The index of the enum entry

Array-Like Interface

See also: Array-Like Interface

EnumWrapper.prototype.length

A read-only property containing the number of entries in the enum.

readonly EnumWrapper.prototype.length: number

EnumWrapper.prototype.[index]

The index signature is implemented on EnumWrapper to allow you to access [key, value] tuples by index like an array. The values accessed by indexing are readonly.

See Order of Iteration for details about the ordering.

readonly EnumWrapper.prototype.[index: number]: EnumWrapper.Entry

Map-Like Interface

See also: Map-Like Interface

EnumWrapper.prototype.size

A read-only property containing the number of entries in the enum.

readonly EnumWrapper.prototype.size: number

EnumWrapper.prototype.keys

Returns an Iterator that will iterate all keys of the enum.

See Order of Iteration for details about the ordering.

EnumWrapper.prototype.keys(): IterableIterator<KeyType>

EnumWrapper.prototype.values

Returns an Iterator that will iterate all values of the enum.

See Order of Iteration for details about the ordering.

EnumWrapper.prototype.values(): IterableIterator<EnumType>

EnumWrapper.prototype.entries

Returns an Iterator that will iterate all [key, value] pairs of the enum.

See Order of Iteration for details about the ordering.

EnumWrapper.prototype.entries(): IterableIterator<EnumWrapper.Entry>

EnumWrapper.prototype.@@iterator

Same as EnumWrapper.prototype.entries.

Allows an EnumWrapper to be directly iterated as a collection of [key, value] tuples.

EnumWrapper.prototype.@@iterator(): IterableIterator<EnumWrapper.Entry>

EnumWrapper.prototype.forEach

Iterates every entry in the enum and calls the provided iteratee function.

See Order of Iteration for details about the ordering.

EnumWrapper.prototype.forEach(
    iteratee: EnumWrapper.Iteratee<void>,
    context?: any
): void
  • iteratee: See EnumWrapper.Iteratee. The return value of this function is ignored.
  • context: If provided, then the value will be used as the this context when executing iteratee.

Iteration

EnumWrapper.prototype.forEach

See EnumWrapper.prototype.forEach in the Map-Like Interface section.

EnumWrapper.prototype.map

Builds and returns a new array containing the results of calling the provided iteratee function on every entry in the enum.

See Order of Iteration for details about the ordering.

EnumWrapper.prototype.map<R>(
    iteratee: EnumWrapper.Iteratee<R>,
    context?: any
): R[]
  • R: Generic type param that indicates the type of entries in the resulting array. If not specified, then it will be inferred from the return type of iteratee.
  • iteratee: See EnumWrapper.Iteratee.
  • context: If provided, then the value will be used as the this context when executing iteratee.

Get Arrays of Enum Data

EnumWrapper.prototype.getKeys

Returns an array of all keys in the enum.

See Order of Iteration for details about the ordering.

EnumWrapper.prototype.getKeys(): KeyType[]

EnumWrapper.prototype.getValues

Returns an array of all values in the enum. If the enum contains any duplicate values, then so will the returned array.

See Order of Iteration for details about the ordering.

EnumWrapper.prototype.getValues(): EnumType[]

EnumWrapper.prototype.getEntries

Returns a list of [key, value] tuples representing all entries in the enum.

See Order of Iteration for details about the ordering.

EnumWrapper.prototype.getEntries(): EnumWrapper.Entry[]

Get Ordered Index of Keys/Values

EnumWrapper.prototype.indexOfKey

Returns the ordered index of a key of the enum. This can be useful for implementing comparators based on the iteration order of the enum, for example.

See Order of Iteration for details about the ordering.

EnumWrapper.prototype.indexOfKey(key: KeyType): number
  • key: A valid key of the enum.

EnumWrapper.prototype.indexOfValue

Returns the ordered index of a value of the enum. This can be useful for implementing comparators based on the iteration order of the enum, for example.

See Order of Iteration for details about the ordering.

EnumWrapper.prototype.indexOfValue(value: EnumType): number
  • value: A valid value of the enum.

Key Validation/Typecasting

EnumWrapper.prototype.isKey

Returns true if the provided key is a valid key for the enum.

Also acts as a type guard to tell the compiler that the provided key is the more specific KeyType type.

EnumWrapper.prototype.isKey(
    key: string | null | undefined
): key is KeyType

EnumWrapper.prototype.asKeyOrThrow

If the provided key is a valid key for the enum, then the key is returned, but cast to the more specific KeyType type.

If the provided key is NOT valid, then an Error is thrown.

EnumWrapper.prototype.asKeyOrThrow(
    key: string | null | undefined
): KeyType

EnumWrapper.prototype.asKeyOrDefault

If the provided key is a valid key for the enum, then the key is returned, but cast to the more specific KeyType type.

If the provided key is NOT valid, then defaultKey is returned.

This method is overloaded so that its return type is as specific as possible, depending on the type of the defaultKey param.

EnumWrapper.prototype.asKeyOrDefault(
    key: string | null | undefined,
    defaultKey?: KeyType | string
): KeyType | string | undefined

Value Validation/Typecasting

EnumWrapper.prototype.isValue

Returns true if the provided value is a valid value for the enum.

Also acts as a type guard to tell the compiler that the provided value is the more specific EnumType type.

EnumWrapper.prototype.isValue(
    value: ValueType | null | undefined
): key is EnumType

EnumWrapper.prototype.asValueOrThrow

If the provided value is a valid value for the enum, then the value is returned, but cast to the more specific EnumType type.

If the provided value is NOT valid, then an Error is thrown.

EnumWrapper.prototype.asValueOrThrow(
    value: ValueType | null | undefined
): EnumType

EnumWrapper.prototype.asValueOrDefault

If the provided value is a valid value for the enum, then the value is returned, but cast to the more specific EnumType type.

If the provided value is NOT valid, then defaultValue is returned.

This method is overloaded so that its return type is as specific as possible, depending on the type of the defaultValue param.

EnumWrapper.prototype.asValueOrDefault(
    value: ValueType | null | undefined,
    defaultValue?: EnumType | ValueType
): EnumType | ValueType | undefined

Lookup Key by Value

EnumWrapper.prototype.getKeyOrThrow

Performs a reverse lookup to get the key that corresponds to the provided value.

If the enum has duplicate values matching the provided value, then the key for the last duplicate entry (in order specified by the Order of Iteration section) is returned.

If the provided value is NOT valid, then an Error is thrown.

EnumWrapper.prototype.getKeyOrThrow(
    value: ValueType | null | undefined
): KeyType

EnumWrapper.prototype.getKeyOrDefault

Performs a reverse lookup to get the key that corresponds to the provided value.

If the enum has duplicate values matching the provided value, then the key for the last duplicate entry (in order specified by the Order of Iteration section) is returned.

If the provided value is NOT valid, then defaultKey is returned.

This method is overloaded so that its return type is as specific as possible, depending on the type of the defaultKey param.

EnumWrapper.prototype.getKeyOrDefault(
    value: ValueType | null | undefined,
    defaultKey?: KeyType | string
): KeyType | string | undefined

Lookup Value by Key

EnumWrapper.prototype.getValueOrThrow

Returns the value corresponding to the provided key.

If the provided key is NOT valid, then an Error is thrown.

EnumWrapper.prototype.getValueOrThrow(
    key: string | null | undefined
): EnumType

EnumWrapper.prototype.getValueOrDefault

Returns the value corresponding to the provided key.

If the provided key is NOT valid, then defaultValue is returned.

This method is overloaded so that its return type is as specific as possible, depending on the type of the defaultValue param.

EnumWrapper.prototype.getValueOrDefault(
    key: string | null | undefined,
    defaultValue?: EnumType | ValueType
): EnumType | ValueType | undefined

Create a new enum-like object with a subset of an enum's entries

EnumWrapper.prototype.createEnumSubset

Use this method to create a new well-typed Enum-Like Object that contains a subset of entries from the original enum.

EnumWrapper.prototype.createEnumSubset(
    ...keys: readonly KeyType[]
): EnumLike

Example:

enum Numbers {
    One = 1,
    Two = 2,
    Three = 3,
    Four = 4
}

const EvenNumbers = $enum(Numbers).createEnumSubset("Two", "Four");
type EvenNumbers = typeof EvenNumbers[keyof typeof EvenNumbers];