ES7 Decorators

decorators.js

class Foo {
  @log
  bar(a, b) {
    console.log(`Adding ${a} and ${b} gives us ${a + b}`); 
  }
}

function log(target, name, descriptor) {
  let fn = descriptor.value;
  
  descriptor.value = function (...args) {
    console.log('Calling', name, 'with', args);
    fn.apply(this, args);
  }
}

const f = new Foo();
f.bar(1, 2);

// Calling bar with [1, 2]
// Adding 1 and 2 gives us 3