Add LastArrayElement, Split, and Trim types (#159)

Co-authored-by: Sindre Sorhus <sindresorhus@gmail.com>
Co-authored-by: Misha Kaletsky <15040698+mmkal@users.noreply.github.com>

base.d.ts

@@ -33,6 +33,7 @@ export {Entry} from './source/entry';
 export {Entries} from './source/entries';
 export {SetReturnType} from './source/set-return-type';
 export {Asyncify} from './source/asyncify';
+export {LastArrayElement} from './source/last-array-element';
 
 // Miscellaneous
 export {PackageJson} from './source/package-json';

readme.md

@@ -104,6 +104,7 @@ Click the type names for complete docs.
 - [`Entries`](source/entries.d.ts) - Create a type that represents the type of the entries of a collection.
 - [`SetReturnType`](source/set-return-type.d.ts) - Create a function type with a return type of your choice and the same parameters as the given function type.
 - [`Asyncify`](source/asyncify.d.ts) - Create an async version of the given function type.
+- [`LastArrayElement`](source/last-array-element.d.ts) - Extracts the type of the last element of an array.
 
 ### Template literal types
 
@@ -114,6 +115,8 @@ Click the type names for complete docs.
 - [`PascalCase`](ts41/pascal-case.d.ts) – Converts a string literal to pascal-case (`FooBar`)
 - [`SnakeCase`](ts41/snake-case.d.ts) – Convert a string literal to snake-case (`foo_bar`).
 - [`DelimiterCase`](ts41/delimiter-case.d.ts) – Convert a string literal to a custom string delimiter casing.
+- [`Split`](ts41/split.d.ts) - Represents an array of strings split using a given character or character set.
+- [`Trim`](ts41/trim.d.ts) - Remove leading and trailing spaces from a string.
 - [`Get`](ts41/get.d.ts) - Get a deeply-nested property from an object using a key path, like [Lodash's `.get()`](https://lodash.com/docs/latest#get) function.
 
 ### Miscellaneous
@@ -132,6 +135,10 @@ Click the type names for complete docs.
 
 ## Tips
 
+### Related
+
+- [typed-query-selector](https://github.com/g-plane/typed-query-selector) - Enhances `document.querySelector` and `document.querySelectorAll` with a template literal type that matches element types returned from an HTML element query selector.
+
 ### Built-in types
 
 There are many advanced types most users don't know about.

source/last-array-element.d.ts

@@ -0,0 +1,23 @@
+/**
+Extracts the type of the last element of an array.
+
+Use-case: Defining the return type of functions that extract the last element of an array, for example [`lodash.last`](https://lodash.com/docs/4.17.15#last).
+
+@example
+```
+import {LastArrayElement} from 'type-fest';
+
+declare function lastOf<V extends any[]>(array: V): LastArrayElement<V>;
+
+const array = ['foo', 2];
+
+typeof lastOf(array);
+//=> number
+```
+*/
+export type LastArrayElement<ValueType extends unknown[]> =
+	ValueType extends [infer ElementType]
+		? ElementType
+		: ValueType extends [infer _, ...infer Tail]
+			? LastArrayElement<Tail>
+			: never;

test-d/last-array-element.ts

@@ -0,0 +1,9 @@
+import {expectType} from 'tsd';
+import {LastArrayElement} from '../ts41';
+
+declare function lastOf<V extends [any, ...any]>(array: V): LastArrayElement<V>;
+const array: ['foo', 2, 'bar'] = ['foo', 2, 'bar'];
+const mixedArray: ['bar', 'foo', 2] = ['bar', 'foo', 2];
+
+expectType<'bar'>(lastOf(array));
+expectType<2>(lastOf(mixedArray));

test-d/split.ts

@@ -0,0 +1,12 @@
+import {expectType} from 'tsd';
+import {Split} from '../ts41';
+
+declare function split<S extends string, D extends string>(string: S, separator: D): Split<S, D>;
+
+const items = 'foo,bar,baz,waldo';
+const array = split(items, ',');
+
+expectType<'foo'>(array[0]);
+expectType<'bar'>(array[1]);
+expectType<'baz'>(array[2]);
+expectType<'waldo'>(array[3]);

test-d/trim.ts

@@ -0,0 +1,10 @@
+import {expectType} from 'tsd';
+import {Trim} from '../ts41';
+
+declare function trim<S extends string>(value: S): Trim<S>;
+
+expectType<'foo'>(trim(' foo'));
+expectType<'bar'>(trim('bar '));
+expectType<'baz'>(trim(' baz '));
+expectType<'waldo'>(trim('  waldo  '));
+expectType<'fr ed'>(trim(' fr ed '));

ts41/index.d.ts

@@ -7,4 +7,6 @@ export {KebabCase} from './kebab-case';
 export {PascalCase} from './pascal-case';
 export {SnakeCase} from './snake-case';
 export {DelimiterCase} from './delimiter-case';
+export {Split} from './split';
+export {Trim} from './trim';
 export {Get} from './get';

ts41/split.d.ts

@@ -0,0 +1,22 @@
+/**
+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 {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, ',');
+```
+*/
+export type Split<S extends string, D extends string> =
+	S extends `${infer T}${D}${infer U}`
+		? [T, ...Split<U, D>]
+		: [S];

ts41/trim.d.ts

@@ -0,0 +1,22 @@
+/**
+Remove spaces from the left side.
+*/
+type TrimLeft<V extends string> = V extends ` ${infer R}` ? TrimLeft<R> : V;
+
+/**
+Remove spaces from the right side.
+*/
+type TrimRight<V extends string> = V extends `${infer R} ` ? TrimRight<R> : V;
+
+/**
+Remove leading and trailing spaces from a string.
+
+@example
+```
+import {Trim} from 'type-fest';
+
+Trim<' foo '>
+//=> 'foo'
+```
+*/
+export type Trim<V extends string> = TrimLeft<TrimRight<V>>;