add has()

readme.md

@@ -21,8 +21,6 @@ if (isXXX(a)) {
 
 ## Functions
 
-### typeof narrowing
-
 - isString
 - isNumber
 - isBigInt
@@ -95,4 +93,40 @@ if (isInstance(a, TestClass)) {
 if (isArray<string>(a)) {
   a[0].trim();
 }
+
+let b: TestClass | undefined | null;
+// b.m(); // Error: Object is possibly 'null' or 'undefined'.ts(2533)
+if (!isNil(b)) {
+  b.m(); // no Error any more
+}
 ```
+
+### has()
+
+```typescript
+type Fish = { swim: () => {} };
+type Bird = { fly: () => {} };
+
+function getPet(): any {
+  return {} as any;
+}
+
+//---------------
+
+let pet: Fish | Bird = getPet(); // Fish | Bird
+
+const isBird = has<Bird>('fly');
+const isFish = has('swim');
+
+if (isBird(pet)) {
+  pet.fly();
+}
+if (isFish(pet)) {
+  pet.swim();
+}
+```
+
+## Version
+
+- 1.1.0
+  - add `has()`

src/index.ts

@@ -47,19 +47,8 @@ export function isArray<T>(value: unknown): value is Array<T> {
   return Array.isArray(value);
 }
 
-// export function as<T>(value: unknown): value is T {
-//   return true;
-// }
-
-// export function is<T>(
-//   typeFuc: (v: unknown) => boolean,
-//   value: unknown
-// ): value is T {
-//   return typeFuc(value);
-// }
-
-export function is<T>(typeFunc: (v: unknown) => boolean) {
+export function has<T>(key: keyof T) {
   return function is(b: unknown): b is T {
-    return typeFunc(b);
+    return !isNil((b as any)[key]);
   };
 }

src/test.ts

@@ -10,7 +10,7 @@ import {
   isInstance,
   isArray,
   isNil,
-  is
+  has
 } from './index';
 
 let a: unknown;
@@ -58,40 +58,29 @@ if (isArray<string>(a)) {
 }
 
 let b: TestClass | undefined | null;
+// b.m(); // Error: Object is possibly 'null' or 'undefined'.ts(2533)
+if (!isNil(b)) {
+  b.m(); // no Error any more
+}
 
-b.m(); // Error: Object is possibly 'null' or 'undefined'.ts(2533)
+/*
+ *  has()
+ */
 
 type Fish = { swim: () => {} };
 type Bird = { fly: () => {} };
 
-function getPet(): Fish | Bird {
+function getPet(): any {
   return {} as any;
 }
 let pet: Fish | Bird = getPet();
 
-// const isFish = is<Fish>(pet, (pet)=>{
-//   return !isNil((pet as Fish).swim);
-// })
-
-// if(isFish(pet)){
-
-//   pet
-
-// }
-
-export function has<T>(key: keyof T) {
-  return function is(b: unknown): b is T {
-    return !isNil((b as any)[key]);
-  };
-}
-
+const isBird = has<Bird>('fly');
 const isFish = has('swim');
 
-if (has('swim')) {
+if (isBird(pet)) {
+  pet.fly();
+}
+if (isFish(pet)) {
+  pet.swim();
 }
-
-// const isFish = is<Fish>((p)=>{ return !isNil((p as any).swim)})
-
-// function isFish2(p):p is Fish{
-//  return !isNil((p as any).swim)
-// }