How to properly check and log http status code using promises and node.js?
Solution 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: ${website}`)
}
})
})
}
Solution 2
Using util.promisify()
, you can convert http.get()
into a promise-based asynchronous method, but first there's some preparation to do since it does not follow the convention of callback(error, response) { ... }
:
const http = require('http')
const { promisify } = require('util')
// define a custom promisified version of `http.get()`
http.get[promisify.custom] = (options) => new Promise(resolve => {
http.get(options, resolve)
});
// convert callback to promise
const httpGet = promisify(http.get)
async function getStatusCodeResult(website) {
const res = await httpGet(website)
const status = res.statusCode
const message = `${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
.
Squanchy
Updated on June 07, 2022Comments
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Squanchy over 1 year
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'] }
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Squanchy over 5 yearsAwesome, can you please explain why the promise wraps the
http.get
is that the way its always used you wrap the referencing environment whit the promise? Also, do you by any chance know why I am only gettingerror error: http://google.com/nothing Success: http://www.google.com/
and not the rest of sites. -
Bergi over 5 yearsYes, you always wrap the asynchronous function within the
new Promise
constructor. How you resolve and reject is usually different though -
Bergi over 5 yearsIf you're not getting anything from the other promises, it's likely that the response were neither 400<=status<500 nor 200<=status<300. If there's a redirect or a server error, you never settle the promise (which is a bad thing!), so neither of your callbacks would run.
-
Patrick Roberts over 5 years@Bergi would it be beneficial for me to add a solution using
util.promisify()
or should I not bother? -
Squanchy over 5 years@Bergi do you think I should post a different question, about not logging all the sites in the sample array only logging
http://google.com/nothing
andhttp://www.google.com/
? -
Bergi over 5 years@PatrickRoberts Please go for it. (Also I didn't check the
http.get
signature in the docs, it's kinda suspicious that there's no error parameter) -
Bergi over 5 yearsI wonder, shouldn't
http.get[promisify.custom]
be native in node already? -
Patrick Roberts over 5 years@Bergi I checked, it's not defined.