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tessl/npm-invert-kv

Utility function for inverting key/value pairs of JavaScript objects

Workspace
tessl
Visibility
Public
Created
Last updated
Describes
npmpkg:npm/invert-kv@4.2.x

To install, run

npx @tessl/cli install tessl/npm-invert-kv@4.2.0

index.mddocs/

Invert KV

Invert KV is a utility function for inverting the key/value pairs of JavaScript objects. It transforms object keys into values and values into keys, supporting both regular properties and symbol properties with robust error handling.

Package Information

  • Package Name: invert-kv
  • Package Type: npm
  • Language: JavaScript with TypeScript definitions
  • Installation: npm install invert-kv

Core Imports

import invertKeyValue from "invert-kv";

The package is ES module only (no CommonJS support).

Basic Usage

import invertKeyValue from "invert-kv";

// Basic object inversion
invertKeyValue({foo: 'bar', hello: 'world'});
//=> {bar: 'foo', world: 'hello'}

// Handles string and number keys
invertKeyValue({foo: 'bar', 1: 'one'});
//=> {bar: 'foo', one: '1'}

// Supports symbols
const sym = Symbol('test');
invertKeyValue({foo: sym, unicorn: 'rainbow'});
//=> {[sym]: 'foo', rainbow: 'unicorn'}

Capabilities

Key-Value Inversion

Inverts the key/value pairs of an object, creating a new object where the original keys become values and the original values become keys.

/**
 * Invert the key/value of an object
 * @param object - The object to invert (must be non-null object)
 * @returns A new object with inverted key/value pairs
 * @throws TypeError if input is not an object or is null
 */
function invertKeyValue<T extends Record<PropertyKey, PropertyKey>>(
  object: T
): {[P in keyof T as T[P]]: keyof T extends number ? Exclude<keyof T, number> | string : P};

The function:

  • Processes both regular object properties (string/number keys) and symbol properties
  • Creates a new object without mutating the original
  • Throws TypeError with message "Expected an object" for invalid inputs (null, undefined, or non-objects)
  • Supports any PropertyKey type for both keys and values (string, number, symbol)

Usage Examples:

import invertKeyValue from "invert-kv";

// String properties
invertKeyValue({foo: 'bar', '🦄': '🌈'});
//=> {bar: 'foo', '🌈': '🦄'}

// Mixed string and number properties
invertKeyValue({name: 'Alice', 1: 'first', 2: 'second'});
//=> {Alice: 'name', first: '1', second: '2'}

// Symbol properties
const mySymbol = Symbol('myKey');
invertKeyValue({regularKey: mySymbol, anotherKey: 'value'});
//=> {[mySymbol]: 'regularKey', value: 'anotherKey'}

// Symbols as keys
const keySymbol = Symbol('keySymbol');
invertKeyValue({[keySymbol]: 'symbolValue', normalKey: 'normalValue'});
//=> {symbolValue: keySymbol, normalValue: 'normalKey'}

// Error handling
try {
  invertKeyValue(null);
} catch (error) {
  console.log(error.message); // "Expected an object"
}

try {
  invertKeyValue("not an object");
} catch (error) {
  console.log(error.message); // "Expected an object"
}

Types

/**
 * Generic type-safe version with mapped types
 */
function invertKeyValue<T extends Record<PropertyKey, PropertyKey>>(
  object: T
): {[P in keyof T as T[P]]: keyof T extends number ? Exclude<keyof T, number> | string : P};

The TypeScript definition provides:

  • Generic constraint T extends Record<PropertyKey, PropertyKey> ensuring both keys and values are valid PropertyKey types
  • Complex mapped type that preserves type relationships after inversion
  • Special handling for numeric keys which become string values in the result
  • Full type safety for the inversion operation