从 Nodejs 传递数据 http 获取请求

Question

I am trying to pass data out of my get request from resp.on function. I want to use 'var url' to make a separate get request from which I will parse data again. I am able to console.log variables from inside the function but not return (or access from outside). This seems to be a scoping or async issue.

const https = require('https');

https.get('https://collectionapi.metmuseum.org/public/collection/v1/objects', (resp) => {
    let data = '';

    // A chunk of data has been recieved.
    resp.on('data', (chunk) => {
      data += chunk;
    });

    // The whole response has been received. Print out the result.
    resp.on('end', () => {
      var json_data = JSON.parse(data);
      var total = json_data.total
      var random_objectID = Math.floor(Math.random()*total)
      var url = 'https://collectionapi.metmuseum.org/public/collection/v1/objects/' + random_objectID
      console.log(url);
    });

  }).on("error", (err) => {
    console.log("Error: " + err.message);
  })

//'url' becomes unknown here. I want to pass it to another get request.

Answer 1

It's both an async and a scope issue!

If you declare var url; in the outermost scope you'll be able to set it inside that callback as intended, but since that's happening asynchronously you won't be able to use the value outside the scope unless you are checking after the callback completes.

Alternatively, you could wrap the whole thing in a promise , eg

const https = require('https');

new Promise((resolve,reject)=>{
  let targetUrl = 'https://collectionapi.metmuseum.org/public/collection/v1/objects';
  https.get(targetUrl,resp=>{
    // ...
    resp.on('end', () => {
      // ...
      resolve(url);
    });
  });
}).then(url=>{
// do stuff with that URL
});

If your goal is to automate fetching data from web resources, I'd recommend checking out the request module , which also has a promisified variant.