✨ Add init function

Closes #112

Author: TomokiMiyauci

src/init.ts

@@ -0,0 +1,37 @@
+// Copyright 2021-present the Fonction authors. All rights reserved. MIT license.
+import { slice } from './slice.ts'
+/**
+ * Returns all but the last element of the given list or string.
+ *
+ * @param val - string or any array object
+ * @returns The result of `val.slice(0, -1)`
+ *
+ * @example
+ * ```ts
+ * // String
+ * init('hello') // 'hell'
+ * init('h') // ''
+ * init('') // ''
+ * ```
+ *
+ * @example
+ * ```ts
+ * init([1, 2, 3]) // [1, 2]
+ * init(['hello', 'world']) // ['hello']
+ * init(['hello']) // []
+ * init([]) // []
+ * ```
+ *
+ * @category `Array` `String`
+ *
+ * @see Related to {@link tail}
+ *
+ * @public
+ */
+const init: {
+  (val: string): string
+  <T extends unknown[]>(val: T): T
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+} = (val: any) => slice(0, -1, val)
+
+export { init }

test/init.ts

@@ -0,0 +1,40 @@
+// Copyright 2021-present the Fonction authors. All rights reserved. MIT license.
+import { assertEquals } from '../dev_deps.ts'
+import { init } from '../src/init.ts'
+
+Deno.test('init', () => {
+  const tableString: [string, string][] = [
+    ['', ''],
+    ['a', ''],
+    ['ab', 'a'],
+    ['abc', 'ab']
+  ]
+  tableString.forEach(([val, expected]) => {
+    assertEquals(init(val), expected, `init(${val}) -> ${expected}`)
+  })
+
+  const tableArray: [unknown[], unknown[]][] = [
+    [[], []],
+    [[''], []],
+    [[undefined], []],
+    [[null], []],
+    [[0], []],
+    [['', ''], ['']],
+    [[0, 0], [0]],
+    [[0, ''], [0]],
+    [['hello', 'world'], ['hello']],
+    [
+      ['hello', 'new', 'world'],
+      ['hello', 'new']
+    ],
+    [
+      [undefined, null, 'hello', 'world'],
+      [undefined, null, 'hello']
+    ],
+    [[['hello', 'world']], []]
+  ]
+
+  tableArray.forEach(([val, expected]) => {
+    assertEquals(init(val), expected, `init(${val}) -> ${expected}`)
+  })
+})