type-fest/source/split.d.ts

A collection of essential TypeScript types

/**
Represents an array of strings split using a given character or character set.

Use-case: Defining the return type of a method like `String.prototype.split`.

@example
```
import type {Split} from 'type-fest';

declare function split<S extends string, D extends string>(string: S, separator: D): Split<S, D>;

type Item = 'foo' | 'bar' | 'baz' | 'waldo';
const items = 'foo,bar,baz,waldo';
let array: Item[];

array = split(items, ',');
```

@category String
@category Template literal
*/
export type Split<
	S extends string,
	Delimiter extends string,
> = SplitHelper<S, Delimiter>;

type SplitHelper<
	S extends string,
	Delimiter extends string,
	Accumulator extends string[] = [],
> = S extends `${infer Head}${Delimiter}${infer Tail}`
	? SplitHelper<Tail, Delimiter, [...Accumulator, Head]>
	: Delimiter extends ''
		? Accumulator
		: [...Accumulator, S];