How to properly check and log http status code using promises and node.js?

问题

I am new to JavaScript and very new to node.js framework, just started using it a few days ago. My apologies if my code is nonsensical, the whole idea of promises and callbacks is still sinking in. That being said my question is the following I am trying to figure out if certain request to websites are successful or cause an error based on the range of their status code response. I am working with an array of websites and what I've done so far is below, I do however get a TypeError: Cannot read property 'then' of undefined on my local machine with node.js installed and can't figure out why.

const sample = [
    'http://www.google.com/',
    'http://www.spotify.com/us/',
    'http://twitter.com/',
    'http://google.com/nothing'
]

const http = require('http')

const getStatusCodeResult = (website) => {

    http.get(website, (res) => {
        return new Promise((resolve, reject) => {
            setTimeout(() => {
                let statusCode = res.statusCode
                error = statusCode >= 400 && statusCode <= 500 ? `error: ${website}`: null
                if (error) {
                    reject(error)
                    
                } else if (statusCode >= 200 && statusCode <= 300) {
                    resolve(`Success: ${website}`)
                }
            }, 0)
        })
    })
}
// LOOP PROMISES
const getAllStatusCodeResult = (websites) => {
    websites.forEach((website) => {
        getStatusCodeResult(website)
            .then((result) => {
                console.log(result)
            })
            .catch(error => {
                console.log('error', error)
            })
    })
}
getAllStatusCodeResult(sample)

Ideally I would want the result to be printed as the example below, but for now I am just using console.log to figure out if the code even works.

   // Example Printout
   {
      success: ['https://www.google.com/', 'https://www.spotify.com/us/', 
      'https://twitter.com /' ],
      error: [''http://google.com/nothing']
   }

回答1:

You mixed up the first two lines. The new Promise wrapper that gets you the value to return needs to be on the outside, and the http.get call should be inside its executor callback. Also you don't really need that timeout:

function getStatusCodeResult(website) {
    return new Promise((resolve, reject) => {
        http.get(website, (res) => {
            let statusCode = res.statusCode,
                error = statusCode >= 400 && statusCode <= 500 ? `error: ${website}`: null
            if (error) {
                reject(error)
            } else if (statusCode >= 200 && statusCode <= 300) {
                resolve(`Success: ${website}`)
            }
        })
    })
}

回答2:

Using util.promisify(), you can convert http.get() into a promise-based asynchronous method, but first there's some preparation to do since it does not follow the convention of callback(error, response) { ... }:

const http = require('http')
const { promisify } = require('util')

// define a custom promisified version of `http.get()`
http.get[promisify.custom] = (options) => new Promise(resolve => {
  http.get(options, resolve)
});

// convert callback to promise
const httpGet = promisify(http.get)

async function getStatusCodeResult(website) {
  const res = await httpGet(website)
  const status = res.statusCode
  const message = `${http.STATUS_CODES[status]}: ${website}`

  if (status >= 400) {
    throw message
  } else {
    return message
  }
}

In addition, you can use http.STATUS_CODES to get the the appropriate message for each possible statusCode rather than returning a vague Error or Success.

来源：https://stackoverflow.com/questions/48941063/how-to-properly-check-and-log-http-status-code-using-promises-and-node-js

标签

javascript

node.js

callback

promise

es6-promise