✨ Add defaultTo function

docs/api/defaultto/index.md

@@ -0,0 +1,30 @@
+<!-- Do not edit this file. It is automatically generated by API Documenter. -->
+
+
+
+## defaultTo variable
+
+> 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.
+> 
+
+Returns the second argument if it is not `null`<!-- -->, `undefined` or `NaN`<!-- -->; otherwise the first argument is returned.
+
+<b>Signature:</b>
+
+```typescript
+defaultTo: <T extends unknown>(a: T) => <U extends unknown>(b: U) => IsNill<U> extends true ? T : IsNumber<U> extends false ? U : T | U
+```
+
+## Example
+
+
+```ts
+const defaultVal = defaultTo('anonymous')
+defaultVal(undefined) // 'anonymous'
+defaultVal(null) // 'anonymous'
+defaultVal(NaN) // 'anonymous'
+
+defaultVal('Tom') // 'Tom'
+
+```
+

docs/api/index.md

@@ -12,6 +12,7 @@
 |  [and](./and/) | Returns true if both arguments are true; otherwise false. |
 |  [append](./append/) | Returns a new list containing the contents of the given list, followed by the given value |
 |  [dec](./dec/) | Decrements its argument. |
+|  [defaultTo](./defaultto/) | <b><i>(BETA)</i></b> Returns the second argument if it is not <code>null</code>, <code>undefined</code> or <code>NaN</code>; otherwise the first argument is returned. |
 |  [divide](./divide/) | Divide its second argument from its first argument. |
 |  [endsWith](./endswith/) | Checks if a string ends with the provided substring. |
 |  [F](./f/) | A function that always returns <code>false</code>. Any passed in parameters are ignored. |
@@ -28,6 +29,7 @@
 |  [isBoolean](./isboolean/) | Whatever argument is type of <code>boolean</code> or not. |
 |  [isEmpty](./isempty/) | Returns <code>true</code> if the given value is its type's empty value; otherwise <code>false</code>. |
 |  [isFunction](./isfunction/) | Whatever argument is type of <code>function</code> or not. |
+|  [isNaN](./isnan/) | <b><i>(BETA)</i></b> Whatever argument is <code>NaN</code> or not. |
 |  [isNill](./isnill/) | Whatever argument is type of <code>undefined</code> or <code>null</code>. |
 |  [isNull](./isnull/) | Whatever argument is type of <code>null</code> or not. |
 |  [isNumber](./isnumber/) | Whatever argument is type of <code>number</code> or not. |

mod.ts

@@ -3,6 +3,7 @@ export { and } from './src/and.ts'
 export { append } from './src/append.ts'
 export { _ } from './src/constants/index.ts'
 export { dec } from './src/dec.ts'
+export { defaultTo } from './src/defaultTo.ts'
 export { divide } from './src/divide.ts'
 export { endsWith } from './src/endsWith.ts'
 export { F } from './src/F.ts'
@@ -19,6 +20,7 @@ export { isBigint } from './src/isBigint.ts'
 export { isBoolean } from './src/isBoolean.ts'
 export { isEmpty } from './src/isEmpty.ts'
 export { isFunction } from './src/isFunction.ts'
+export { isNaN } from './src/isNaN.ts'
 export { isNill } from './src/isNill.ts'
 export { isNull } from './src/isNull.ts'
 export { isNumber } from './src/isNumber.ts'

src/defaultTo.ts

@@ -0,0 +1,34 @@
+import { isNaN } from './isNaN.ts'
+import { IsNill, isNill } from './isNill.ts'
+import { IsNumber } from './isNumber.ts'
+import { or } from './or.ts'
+
+/**
+ * Returns the second argument if it is not `null`, `undefined` or `NaN`; otherwise the first argument is returned.
+ *
+ * @param a - `a` will be returned instead of `default`
+ * @returns Returns a function that stores the default `a` value. The function accept `b` argument.
+ * if `b` is `null`, `undefined` or `NaN`, return `a`; otherwise return `b`
+ *
+ * @example
+ * ```ts
+ * const defaultVal = defaultTo('anonymous')
+ * defaultVal(undefined) // 'anonymous'
+ * defaultVal(null) // 'anonymous'
+ * defaultVal(NaN) // 'anonymous'
+ *
+ * defaultVal('Tom') // 'Tom'
+ * ```
+ *
+ * @beta
+ */
+const defaultTo = <T extends unknown>(a: T) => <U extends unknown>(
+  b: U
+): IsNill<U> extends true ? T : IsNumber<U> extends false ? U : T | U =>
+  (or(isNill(b), isNaN(b)) ? a : b) as IsNill<U> extends true
+    ? T
+    : IsNumber<U> extends false
+    ? U
+    : T | U
+
+export { defaultTo }

test/defaultTo.spec.ts

@@ -0,0 +1,20 @@
+import { defaultTo } from '@/defaultTo'
+
+describe('defaultTo', () => {
+  const defaultValue = 'hello'
+  const table: [unknown, unknown, unknown][] = [
+    [defaultValue, '', ''],
+    [defaultValue, 'world', 'world'],
+    [defaultValue, undefined, defaultValue],
+    [defaultValue, null, defaultValue],
+    [defaultValue, NaN, defaultValue],
+    [defaultValue, NaN, defaultValue],
+    [defaultValue, 0, 0],
+    [defaultValue, {}, {}],
+    [defaultValue, [], []]
+  ]
+
+  it.each(table)('defaultTo(%s, %s) -> %s', (a, b, expected) => {
+    expect(defaultTo(a)(b)).toEqual(expected)
+  })
+})