feat(decorators): Add once decorator

Invoke the decorated function only once

README.md

@@ -48,13 +48,25 @@ class Test {
 }
 ```
 
+`once` - Add `once` functionality to the method
+```ts
+import { once } from 'helpful-decorators';
+
+class Test {
+ @once
+ method() {
+   // This will run only once
+ }
+}
+```
+
 ### Roadmap
 
  - ~~timeout~~
  - ~~debounce~~
  - ~~throttle~~
+ - ~~once~~
  - memoize
- - once
  - ...
 
 License

__tests__/decorators.spec.ts

@@ -1,12 +1,12 @@
-import { timeout, debounce, throttle } from '../src';
+import { timeout, debounce, throttle, once } from '../src';
 jest.mock('lodash.debounce');
 jest.mock('lodash.throttle');
 import * as throttleFn from 'lodash.throttle';
 import * as debounceFn from 'lodash.debounce';
 jest.useFakeTimers();
 
-describe('Decorators', () => {
 
+describe('Decorators', () => {
   describe('timeout', function () {
     class Test {
       @timeout(1000)
@@ -70,5 +70,23 @@ describe('Decorators', () => {
       expect(debounceFn['mock'].calls[0][1]).toEqual(3000);
       expect(debounceFn['mock'].calls[0][2]).toEqual({});
     });
+  });
+
+  describe('once', function () {
+    class TestOnce {
+      @once
+      method() {
+        console.warn('Once Worked!');
+      }
+    }
+    it('should call the method only once', function () {
+      const instance = new TestOnce();
+      const consoleSpy = jest.spyOn(console, 'warn');
+      instance.method();
+      instance.method();
+      instance.method();
+      expect(consoleSpy).toBeCalled();
+      expect(consoleSpy).toHaveBeenCalledTimes(1);
+    });
   })
 });

package.json

@@ -36,7 +36,8 @@
   "keywords": [
     "decorators",
     "setTimeout decorator",
-    "debounce decorator"
+    "debounce decorator",
+    "once decorator"
   ],
   "devDependencies": {
     "@types/jest": "^20.0.8",
@@ -51,6 +52,7 @@
   "dependencies": {
     "conventional-changelog-cli": "^1.3.3",
     "lodash.debounce": "^4.0.8",
+    "lodash.once": "^4.1.1",
     "lodash.throttle": "^4.1.1"
   }
 }

src/index.ts

@@ -1,3 +1,4 @@
 export { timeout } from './timeout';
 export { debounce } from './debounce';
-export { throttle } from './throttle';
+export { throttle } from './throttle';
+export { once } from './once';

src/once.ts

@@ -0,0 +1,16 @@
+import * as onceFn from 'lodash.once';
+
+/**
+ * 
+ * 
+ * @export
+ * @param {*} target 
+ * @param {string} propertyKey 
+ * @param {PropertyDescriptor} descriptor 
+ * @returns 
+ */
+export function once ( target : any, propertyKey : string, descriptor : PropertyDescriptor ) {
+  const originalMethod = descriptor.value;
+  descriptor.value = onceFn(originalMethod);
+  return descriptor;
+}

tsconfig.json

@@ -6,6 +6,7 @@
     "declaration": true,
     "outDir": "./dist",      
     "noImplicitAny": false,
+    "experimentalDecorators": true,
     "strict": true,                
     "noUnusedLocals": true,
     "noEmitOnError": true,