如何理解一下代码中的this指向

function* objectEntries() {

  let propKeys = Object.keys(this);



  for (let propKey of propKeys) {

    yield [propKey, this[propKey]];

  }

}



let jane = { first: 'Jane', last: 'Doe' };



jane[Symbol.iterator] = objectEntries;



for (let [key, value] of jane) {

  console.log(`${key}: ${value}`);

}