NodeJS使用Promise的正确方法

Question

I have two simple functions:

  function GetLinks() {
      return new Promise(function(resolve) {
     request(options, function (error, response, body) {
         if (!error && response.statusCode == 200) {
             // Print out the response body
             let rawcookies = response.headers['set-cookie'];
             const $ = cheerio.load(body)

             $('.entry-title a[href]').each((index, elem) => {

                 let newItem = (index, $(elem).attr('href'))
                 listOfArticleLinks.push(newItem);

             });

             listOfArticleLinks.forEach(function (item, index, array) {
                 console.log(item);
             });

             resolve();

         }

})})}

The function GetLinks() sends a request to URL, parse links, add them to the array and write in the console. After writing in the console I call resolve() function as Promise is fulfilled.

The second function is:

function PrintMe() {
    const initializePromise = GetLinks();
    initializePromise.then(function()
    {
       console.log("it's done");
    })
}

The function PrintMe() should simply print it's done after GetLinks() prints all links to the console.

I'm calling them in this order:

GetLinks();
PrintMe();

The problem is that sometimes "it's done" is printed in the middle of links and sometimes on the end. Why it does not print "it's done" always on the end? My goal is to wait for GetLinks to be fully finished and then simply call another function.

Answer 1

From what you've posted I can only give you this much of an answers:

function GetLinks() {
  // const options = ... // fill in your option here
  return promisifiedRequest(options).then(({response, body}) => {
    let rawcookies = response.headers["set-cookie"]; // unused variable?
    const $ = cheerio.load(body);

    $(".entry-title a[href]").each((index, el) => {
      console.log($(elem).attr("href"));
    });
  });
}

function printMe() {
  console.log("It's done!");
}

// this is your old plain request, but wrapped in a promise
function promisifiedRequest(options) {
  return new Promise(function(resolve, reject) {
    request(options, function(error, response, body) {
      if (!error && response.statusCode == 200) {
        // what is passed here is going to be
        // available in .then call
        resolve({ response, body });
      } else {
        reject("Oopps, can't request");
      }
    });
  });
}

GetLinks()
  .then(printMe)
  .catch(error => console.error(error)); // handle errors

Answer 2

getLinks is making a request. printMe is calling getLinks inside of it again and that's why two promises overlap. Change printMe so that it only prints something.

And then call them like this.

getLinks().then(printMe)