JS Decorators How to example

decorators.js

// Prop/Method Decorator with no arguments
function logDecorator(t, n, descriptor) {
  const original = descriptor.value;
  if (typeof original === 'function') {
    descriptor.value = function(...args) {
      console.log(`Arguments: ${args}`);
      try {
        const result = original.apply(this, args);
        console.log(`Result: ${result}`);
        return result;
      } catch (e) {
        console.log(`Error: ${e}`);
        throw e;
      }
    }
  }
  return descriptor;
};

/** Usage
 *
 * @logDecorator
 * function toto () {}
 */

// Prop/Method Decorator with a 'name' Arguments
function logDecoratorWithArgs(name) {
  function decorator(t, n, descriptor) {
    const original = descriptor.value;
    if (typeof original === 'function') {
      descriptor.value = function(...args) {
        console.log(`Arguments for ${name}: ${args}`);
        try {
          const result = original.apply(this, args);
          console.log(`Result from ${name}: ${result}`);
          return result;
        } catch (e) {
          console.log(`Error from ${name}: ${e}`);
          throw e;
        }
      }
    }
    return descriptor;
  }
}

/** Usage
 *
 * @logDecoratorWithArgs('some name')
 * function toto () {}
 */


// Class decorator
function log(Class) {
  return (...args) => {
    console.log(args);
    return new Class(...args);
  };
}

/** Usage
 *
 * @log
 * class Example {
 *  constructor(name, age) {
 *  }
 * }
 *
 * const e = new Example('Graham', 34);
 * // [ 'Graham', 34 ]
 * console.log(e);
 * // Example {}
 */