✨ Add trimLeft function

docs/api/index.md

@@ -1531,6 +1531,33 @@ trim('   hello   ') // 'hello'
 ```
 
 
+### trimLeft
+
+<span class="tag beta">beta</span>
+
+
+Removes space from left ends of the string.
+::: warning
+This API is provided as a preview for developers and may change based on feedback that we receive.
+Do not use this API in a production environment.
+:::
+
+
+
+**Signature:**
+
+```ts
+trimLeft: <T extends string>(val: T) => TrimLeft<T>
+```
+
+#### Example 
+
+```ts
+trimLeft('   hello') // 'hello'
+trimLeft(' \n\thello') // 'hello'
+```
+
+
 ### upperCase
 
 
@@ -1755,3 +1782,49 @@ type Primitive = string | number | bigint | boolean | symbol | undefined | null;
 ```
 
 
+### Space
+
+<span class="tag beta">beta</span>
+
+
+Alias for Space values.
+::: warning
+This API is provided as a preview for developers and may change based on feedback that we receive.
+Do not use this API in a production environment.
+:::
+
+
+
+**Signature:**
+
+```ts
+type Space = " " | "\n" | "\t";
+```
+
+
+### TrimLeft
+
+<span class="tag beta">beta</span>
+
+
+Infer the string with the left ends of trimmed.
+::: warning
+This API is provided as a preview for developers and may change based on feedback that we receive.
+Do not use this API in a production environment.
+:::
+
+
+
+**Signature:**
+
+```ts
+type TrimLeft<T extends string> = T extends `${Space}${infer R}` ? TrimLeft<R> : T;
+```
+
+#### Example 
+
+```ts
+TrimLeft<' \n\thello'> // 'hello'
+```
+
+

mod.ts

@@ -52,7 +52,16 @@ export { sum } from './src/sum.ts'
 export { T } from './src/T.ts'
 export { tail } from './src/tail.ts'
 export { trim } from './src/trim.ts'
-export type { AnyFn, Empty, Falsy, Ord, Primitive } from './src/types/index.ts'
+export type { TrimLeft } from './src/trimLeft.ts'
+export { trimLeft } from './src/trimLeft.ts'
+export type {
+  AnyFn,
+  Empty,
+  Falsy,
+  Ord,
+  Primitive,
+  Space
+} from './src/types/index.ts'
 export { upperCase } from './src/upperCase.ts'
 export { values } from './src/values.ts'
 export { xor } from './src/xor.ts'

src/trimLeft.ts

@@ -0,0 +1,49 @@
+import { Space } from './types/index.ts'
+
+/**
+ * Infer the string with the left ends of trimmed.
+ *
+ * @returns String left ends of trimmed
+ *
+ * @remarks
+ * The definition of space
+ * - `''`
+ * - `\n`
+ * - `\t`
+ *
+ * @example
+ * ```ts
+ * TrimLeft<' \n\thello'> // 'hello'
+ * ```
+ *
+ * @beta
+ */
+type TrimLeft<T extends string> = T extends `${Space}${infer R}`
+  ? TrimLeft<R>
+  : T
+
+/**
+ * Removes space from left ends of the string.
+ *
+ * @param val - input string
+ * @returns The result of `val.trimLeft()`
+ *
+ * @remarks
+ * The definition of space
+ * - `''`
+ * - `\n`
+ * - `\t`
+ *
+ * @example
+ * ```ts
+ * trimLeft('   hello') // 'hello'
+ * trimLeft(' \n\thello') // 'hello'
+ * ```
+ *
+ * @beta
+ */
+const trimLeft = <T extends string>(val: T): TrimLeft<T> =>
+  val.trimLeft() as TrimLeft<T>
+
+export { trimLeft }
+export type { TrimLeft }

src/types/index.ts

@@ -45,5 +45,12 @@ export type Empty = '' | [] | {}
  */
 export type Falsy = false | '' | 0 | null | undefined
 
+/**
+ * Alias for Space values.
+ *
+ * @beta
+ */
+export type Space = ' ' | '\n' | '\t'
+
 export type InferArray<T> = T extends (infer R)[] ? R : never
 export type Whitespace = ' ' | '\t' | '\n'

test/trimLeft.test.ts

@@ -0,0 +1,32 @@
+import { assertEquals } from '../deps.ts'
+import { TrimLeft, trimLeft } from '../src/trimLeft.ts'
+import { assertEqual } from './asserts.ts'
+
+Deno.test('trimLeft', () => {
+  const table: [string, string][] = [
+    ['', ''],
+    ['         ', ''],
+    ['\n\n', ''],
+    ['\t\t\t\t', ''],
+    ['hello', 'hello'],
+    [' hello', 'hello'],
+    ['hello ', 'hello '],
+    [' hello ', 'hello '],
+    ['   hello   ', 'hello   '],
+    ['   hello  world  ', 'hello  world  '],
+    ['   hello  world\n\n', 'hello  world\n\n']
+  ]
+  table.forEach(([val, expected]) => {
+    assertEquals(trimLeft(val), expected, `trimLeft(${val}) -> ${expected}`)
+  })
+})
+
+Deno.test('types', () => {
+  assertEqual<'', TrimLeft<''>>()
+  assertEqual<'hello', TrimLeft<'hello'>>()
+  assertEqual<'', TrimLeft<'\n'>>()
+  assertEqual<'', TrimLeft<'\t'>>()
+  assertEqual<'', TrimLeft<'\t\n '>>()
+  assertEqual<'hello ', TrimLeft<'hello '>>()
+  assertEqual<'hello\n\t ', TrimLeft<'\n\t hello\n\t '>>()
+})