arrow func

arrowfunc.js

var asyncFunction = (param, callback) => {
  window.setTimeout(() => {
    callback(param);
  }, 1);
};

var o = {
  doSomething: function () {
    // Here we pass `o` into the async function, 
    // expecting it back as `param`. 
    //
    // Because this arrow function is created within  
    // the scope of `doSomething` it is bound to this 
    // lexical scope.
    asyncFunction(o, (param) => {
      console.log('param === this?', param === this);
    });
  }
};

o.doSomething(); // param === this? true