Create gen_call_before.ts

Author: Mqxx

src/decorator/gen_call_before.ts

@@ -0,0 +1,69 @@
+/**
+ * This function generator generates a class method decorator, that calls a function before the
+ * class method gets called.
+ * 
+ * @example
+ * ```ts
+ * const RunBefore = genCallBefore<Foo>((instance) => {
+ *   if (instance.logging) {
+ *     console.log('Run before method call!');
+ *   }
+ * });
+ * 
+ * class Foo {
+ *   public logging : boolean;
+ * 
+ *   constructor() {
+ *     this.logging = false;
+ *   }
+ * 
+ *   public enableLogging() {
+ *     this.logging = true;
+ *   }
+ * 
+ *   @RunBefore
+ *   public hello() {
+ *     console.log('Hello');
+ *   }
+ * }
+ * 
+ * const logger = new Foo();
+ * 
+ * logger.hello();
+ * // Hello
+ * logger.enableLogging();
+ * logger.hello();
+ * // Run before method call!
+ * // Hello
+ * ```
+ * @param callbackFn Function to call before class method
+ * @returns The decorator function.
+ */
+export function genCallBefore<Class>(
+  callbackFn : (instance : Class, ...args : Array<unknown>) => void
+) : <
+  MethodArguments extends Array<unknown>,
+  MethodReturn extends unknown
+>(
+  method : (this: Class, ...args : MethodArguments) => MethodReturn,
+  _context : ClassMethodDecoratorContext<
+    Class,
+    (this : Class, ...args : MethodArguments) => MethodReturn
+  >
+) => (this : Class, ...args : MethodArguments) => MethodReturn {
+  return function callBefore<
+    MethodArguments extends Array<unknown>,
+    MethodReturn extends unknown
+  >(
+    method : (this : Class, ...args : MethodArguments) => MethodReturn,
+    _context : ClassMethodDecoratorContext<
+      Class,
+      (this : Class, ...args : MethodArguments) => MethodReturn
+    >
+  ) : (this : Class, ...args : MethodArguments) => MethodReturn {
+    return function decorator(this : Class, ...args : MethodArguments) : MethodReturn {
+      callbackFn(this, ...args);
+      return method.call(this, ...args);
+    };
+  };
+}