Inline Switch

A flexible inline switch statement with pattern matching for TypeScript/JavaScript.

Installation

npm install inlineswitch

Features

• Match against exact values, arrays of values, or predicate functions
• Type-safe with full TypeScript support
• More concise and readable than long if-else chains
• Supports default handlers for non-matching cases
• Checks for duplicate case values
• Tiny library with zero dependencies

Usage

Basic Usage

import { inlineSwitch } from "inlineswitch";

const result = inlineSwitch(
  value,
  [
    [5, (v) => `Exact match: ${v}`],
    [[1, 2, 3], (v) => `Array match: ${v}`],
    [(v) => v > 10, (v) => `Predicate match: ${v}`],
  ],
  (v) => `Default: ${v}` // Optional default handler
);

Different Types of Patterns

// Exact value matching
const dayName = inlineSwitch(
  dayNumber,
  [
    [0, () => "Sunday"],
    [1, () => "Monday"],
    [2, () => "Tuesday"],
    [3, () => "Wednesday"],
    [4, () => "Thursday"],
    [5, () => "Friday"],
    [6, () => "Saturday"],
  ],
  () => "Invalid day"
);

// Array matching
const fruitCategory = inlineSwitch(
  fruit,
  [
    [["apple", "pear"], () => "pome"],
    [["peach", "plum", "cherry"], () => "drupe"],
    [["grape", "blueberry"], () => "berry"],
  ],
  () => "other"
);

// Predicate function matching
const sizeCategory = inlineSwitch(length, [
  [(v) => v < 10, () => "small"],
  [(v) => v >= 10 && v < 100, () => "medium"],
  [(v) => v >= 100, () => "large"],
]);

Shorthand for Simple Cases

import { switchValue } from "inlineswitch";

// Simpler syntax for value-only checks
const result = switchValue(
  color,
  ["red", () => "#FF0000"],
  ["green", () => "#00FF00"],
  ["blue", () => "#0000FF"]
);

API

inlineSwitch<T, R>(value: T, cases: SwitchCase<T, R>[], defaultHandler?: CaseHandler<T, R>): R | undefined

The main function that implements pattern matching.

• value: The value to match against case patterns
• cases: An array of case patterns and their handlers
• defaultHandler: Optional default handler if no cases match
• Returns the result of the matched handler or the default handler, or undefined

switchValue<T, R>(value: T, ...cases: Array<[T | T[], CaseHandler<T, R>]>): R | undefined

A shorthand version for simple value-only checks.

Types

type CasePattern<T> = T | T[] | ((value: T) => boolean);
type CaseHandler<T, R> = (value: T) => R;
type SwitchCase<T, R> = [CasePattern<T>, CaseHandler<T, R>];

Error Handling

The library throws a DuplicateCaseError when duplicate case values are detected.

License

MIT