Question

我目前正在尝试理解Node和回调，并尝试了各种解决方案以使其工作，但是param2未定义。谁能告诉我为什么？以及如何解决这个问题？谢谢！

function getPage(callback) {

  url = 'http://www.google.com';

  if (url) {
    url = url;
  } else {
    console.log('There was an error. No URL submitted');
  }

  callback(url, param2);
}

function CB(url, param2) {
console.log(`The URL of the page requested was ${url} and the added argument          was ${param2}`);
}

 getPage(CB);

Answer 1

这是因为param2 在您调用回调函数的范围内未定义。要定位param2，请确保在param2

中初始化getpage()

function getPage(callback) {

  url = 'http://www.google.com';
  // **make sure param2 is defined**
  var param2 = "param2 value"

  if (url) {
    url = url;
  } else {
    console.log('There was an error. No URL submitted');
  }

  callback(url, param2);
}

function CB(url, param2) {
console.log(`The URL of the page requested was ${url} and the added argument was ${param2}`);
}

 getPage(CB);

Answer 2

在getPage函数中，定义param2并将其传递给

节点回调 - 为什么这不起作用？

2 个答案: