refactor: enhance typeguard function type (#211)

* refactor: convert to generic function

* refactor: enhance isArray

Author: rojiwon123

src/isArray.ts

@@ -1,3 +1,5 @@
+import type Include from "./types/Include";
+
 /**
  * Returns true if `a` is an Array.
  *
@@ -7,8 +9,7 @@
  * isArray(2); // false
  * ```
  */
-function isArray(a: any): a is any[] {
-  return Array.isArray(a);
-}
+const isArray = <T>(a: T): a is Include<T, unknown[] | Readonly<unknown[]>> =>
+  Array.isArray(a);
 
 export default isArray;

src/isBoolean.ts

@@ -1,3 +1,5 @@
+import type Include from "./types/Include";
+
 /**
  * Returns true if `n` is a Boolean.
  *
@@ -8,8 +10,6 @@
  * isBoolean("FxTS"); // false
  * ```
  */
-function isBoolean(n: unknown): n is boolean {
-  return typeof n === "boolean";
-}
+const isBoolean = <T>(n: T): n is Include<T, boolean> => typeof n === "boolean";
 
 export default isBoolean;

src/isEmpty.ts

@@ -19,7 +19,7 @@ import isNil from "./isNil";
  * isEmpty(new Date()) // false
  * ```
  */
-export const isEmpty = (value: unknown): boolean => {
+const isEmpty = <T>(value: T): boolean => {
   if (isNil(value)) return true; // if value is null or undefined.
 
   if (

src/isNil.ts

@@ -1,7 +1,6 @@
 import isNull from "./isNull";
 import isUndefined from "./isUndefined";
-
-type Nullable<T> = T extends null | undefined ? T : never;
+import type Include from "./types/Include";
 
 /**
  * Checks if the given value is `null` or `undefined`.
@@ -14,6 +13,7 @@ type Nullable<T> = T extends null | undefined ? T : never;
  * isNil(null); // true
  * ```
  */
-const isNil = <T>(a: T): a is Nullable<T> => isUndefined(a) || isNull(a);
+const isNil = <T>(a: T): a is Include<T, null | undefined> =>
+  isUndefined(a) || isNull(a);
 
 export default isNil;

src/isNull.ts

@@ -1,3 +1,5 @@
+import type Include from "./types/Include";
+
 /**
  * Checks if the given value is `null`.
  *
@@ -9,6 +11,6 @@
  * isNull(null); // true
  * ```
  */
-const isNull = <T>(input: T | null): input is null => input === null;
+const isNull = <T>(input: T): input is Include<T, null> => input === null;
 
 export default isNull;

src/isNumber.ts

@@ -1,3 +1,5 @@
+import type Include from "./types/Include";
+
 /**
  * Returns true if `n` is a Number.
  *
@@ -7,8 +9,6 @@
  * isNumber("a"); // false
  * ```
  */
-function isNumber(n: unknown): n is number {
-  return typeof n === "number";
-}
+const isNumber = <T>(n: T): n is Include<T, number> => typeof n === "number";
 
 export default isNumber;

src/isObject.ts

@@ -1,4 +1,4 @@
-type IdentityObject<T> = T extends object ? T : never;
+import type Include from "./types/Include";
 
 /**
  * Checks if value is the type of object.
@@ -12,9 +12,9 @@ type IdentityObject<T> = T extends object ? T : never;
  * isObject(123); // false
  * ```
  */
-function isObject<T = unknown>(a: T): a is IdentityObject<T> {
+const isObject = <T>(a: T): a is Include<T, object> => {
   const type = typeof a;
   return a != null && (type === "object" || type === "function");
-}
+};
 
 export default isObject;

src/isString.ts

@@ -1,3 +1,5 @@
+import type Include from "./types/Include";
+
 /**
  * Returns true if `s` is a String.
  *
@@ -7,8 +9,6 @@
  * isString(2); // false
  * ```
  */
-function isString(s: unknown): s is string {
-  return typeof s === "string";
-}
+const isString = <T>(s: T): s is Include<T, string> => typeof s === "string";
 
 export default isString;

src/isUndefined.ts

@@ -1,3 +1,5 @@
+import type Include from "./types/Include";
+
 /**
  * Checks if the given value is `undefined`.
  *
@@ -7,6 +9,6 @@
  * isUndefined(2); // false
  * ```
  */
-const isUndefined = <T>(a: T | undefined): a is undefined => a === undefined;
+const isUndefined = <T>(a: T): a is Include<T, undefined> => a === undefined;
 
 export default isUndefined;

src/last.ts

@@ -47,7 +47,7 @@ function last<T extends Iterable<unknown> | AsyncIterable<unknown>>(
   iterable: T,
 ): LastReturnType<T>;
 
-function last<A>(iterable: Iterable<A> | AsyncIterable<A>) {
+function last<A>(iterable: Iterable<A> | AsyncIterable<A> | A[]) {
   if (isArray(iterable) || isString(iterable)) {
     return iterable[iterable.length - 1];
   }