Is there any easy way to do recursive call using promise. Here is my sample.
function getData() {
var result=[];
var deferred = Q.defer();
(function fetchData(pageno){
var options = {
method : 'GET',
url : 'example.com/test',
qs:{
pageNo: pageno
}
}
request(options, function (error, response, body) {
if (error)throw new Error(error);
if (body.hasMorePage == true) { //checking is there next page
result.push(body)
fetchData(++body.pageno); // getting next page data
} else {
deferred.resolve(result); // promise resolve when there is no more page
}
});
})(0);
return deferred.promise;
}
getData().then(function(data){
console.log(data)
});
Let's consider API is giving more data in consecutive calls. in order to collect all the data, I need to use some parameter (EX:hasMorePage) from previous call response. I need to go regressive call only for obtaining this scenario, but I would like to know a better(Promise) way.
Most welcome.
async function request(options, callback) {
// simulate server response of example.com/test with 1 second delay
const totalNumberOfPages = 3;
const pageNo = options.qs.pageNo;
await new Promise(resolve => setTimeout(resolve, 1000));
const hasMorePages = pageNo < totalNumberOfPages;
const body = { hasMorePages };
callback(void 0, { body }, body);
}
function getPage(pageNo) {
const options = {
method: 'GET',
url: 'example.com/test',
qs: { pageNo }
};
return new Promise(resolve => request(options, (error, response, body) => {
console.log('response received', response);
if(error) {
throw new Error(error);
}
resolve(body);
}));
}
async function getData() {
const result = [];
for(let i = 1, hasMorePages = true; hasMorePages; i++) {
const body = await getPage(i);
result.push(body);
hasMorePages = body.hasMorePages;
}
return result;
}
getData().then(data => console.log('RESULT', data));
Related
This question already has answers here:
How do I return the response from an asynchronous call?
(41 answers)
Closed 3 years ago.
In that code, console.log(game) gives me an array, but return(game) gives me null.
I don't know, what should I do to gain that array
takeApi: async (root, args, { req }, info) =>{
let userNick='Izyi';
var request = require('request');
var JsonFind=require('json-find');
var url = 'https://someapi/'+userNick;
var game;
request.get({
url: url,
json: true,
headers: {'API-KEY': 'XXX'}
}, (err, res, data) => {
if (err) {
console.log('Error:', err);
} else if (res.statusCode !== 200) {
console.log('Status:', res.statusCode);
} else {
const doc= JsonFind(data.lifeTimeStats);
var matchesPlayed=(doc.checkKey('7').value);
var wins=(doc.checkKey('8').value);
var kills=(doc.checkKey('10').value);
game ={kills:kills,wins:wins,matchesPlayed:matchesPlayed}
console.log(game);
return(game);
}
})
return(game);
}
request.get works via a callback and is not directly compatible with async/await. That callback happens when the request is done or has errored out. The return(game); then happens before the request has completed.
You need to return a new Promise and then resovle or reject based on the results passed to the callback.
You can then await or .then takeApi and expect to have a value returned.
const takeApi = async(root, args, { req }, info) => {
let userNick = 'Izyi';
var request = require('request');
var JsonFind = require('json-find');
var url = 'https://someapi/' + userNick;
// return a Promise, which will work
// by the called using `await` or `.then`
return new Promise((resolve, reject) => {
request.get({
url: url,
json: true,
headers: {
'API-KEY': 'XXX'
}
}, (err, res, data) => {
if (err) {
console.log('Error:', err);
// error, reject
reject(err);
} else if (res.statusCode !== 200) {
console.log('Status:', res.statusCode);
// error, reject
reject(res.statusCode);
} else {
const doc = JsonFind(data.lifeTimeStats);
var matchesPlayed = (doc.checkKey('7').value);
var wins = (doc.checkKey('8').value);
var kills = (doc.checkKey('10').value);
const game = {
kills: kills,
wins: wins,
matchesPlayed: matchesPlayed
}
console.log(game);
// success, resolve
resolve(game);
}
})
});
}
I have using a code snippet which will return a value after post rest call to an api.
But where ever i am calling the function its not returning the value and prints undefined.
when ever i will call any where getAccessToken(), its says undefiuned, but ifi print the value am getting the output.
How do the called will get the return value, do i need to change anything in the below code.
Thanks
var getAccessToken = exports.getAccessToken = function (res) {
// body...
const request = require('request');
const authKey='EAcEa4o4SkBLo9IpZpW4Y7oDn7d6b30GlouNh28pJ6Q='
const ContentType='application/x-www-form-urlencoded' ;
var postData={
'grant_type':'client_credentials'
};
const options = {
url: 'https://xyz/v1/login',
method: 'POST',
headers: {
'Content-Type': ContentType,
'Authorization':authKey
},
body:require('querystring').stringify(postData)
};
var token;
request(options, function(errror, response, body) {
//console.log(JSON.parse(body));
token= JSON.parse(body).access_token;
});
return token;
}
Your function doesn't return anything. You may use async/await, promises or callbacks to fix it.
exports.getAccessToken = async (res) => {
...
return await request(...)
}
OR
exports.getAccessToken = function(res) {
...
return new Promise(function(resolve, reject) {
...
request(options, function(errror, response, body) {
var token = JSON.parse(body).access_token;
resolve(token);
}
});
}
// Use it like
getAccessToken().then(function(token) { ... });
OR
exports.getAccessToken = function(res, cb) {
...
request(options, function(errror, response, body) {
var token = JSON.parse(body).access_token;
cb(token);
}
}
// Use it like
getAccessToken(res, function(token) { ... });
var request = require('request');
var boardsCall = {
method: 'GET',
url: 'https://api.trello.com/1/organizations/xxxxxxxxxx/boards?filter=open&fields=id,name',
qs: {
key: 'xxxxxxxxxxxxxxxx',
token: 'xxxxxxxxxxxxxxxxxxxxxxxxx'
}
};
function test(url, callback) {
request(url, function(error, response, body) {
if (error) {
return callback(error);
}
callback(null, JSON.parse(body));
})
}
const x = test(boardsCall, function(err, body) {
if (err) {
console.log(err);
}
else {
return body;
}
})
console.log(x);
how can I use the value of the body outside?
to use it in other methods later
I am open to any changes best practices, I read a lot and got a bit confused on the topic of callbacks, promises async await.
In my approach request is wrapped with Promise, test function returns Promise response. Inside the main method test function will be executed synchronously. Once the response value assigned to x do remaining processing logic inside the main() method.
var request = require('request');
var boardsCall = {
method: 'GET',
url: 'https://api.trello.com/1/organizations/xxxxxxxxxx/boards?filter=open&fields=id,name',
qs: {
key: 'xxxxxxxxxxxxxxxx',
token: 'xxxxxxxxxxxxxxxxxxxxxxxxx'
}
};
function test(url) {
//Wrapping request callback with Promise
return new Promise((res, rej)=> {
request(url, function(error, response, body) {
if (error) {
rej(error);
}
res(JSON.parse(body));
})
})
}
async function main() {
try {
const x = await test(boardsCall);
console.log("Result : ", x );
// Remaining logic to process based on x value
} catch(e) {
console.error("Error :", e);
}
}
//Calling main method
main()
My async function enters then before request is completed. Shouldn't Then part of the code executes only after the async function is completed? How to make the function call only when all the function has finished executing?
app.js
var request_test = require('./request_test');
baseUrl = "https://github.com";
promiseFunction().then((result)=>{
console.log("complete")
});
var promiseFunction = async function promiseFunction() {
request_test.request_test(baseUrl);
}
request_test.js
var request = require('request');
var cheerio = require('cheerio');
var request_test = function check(baseUrl) {
console.log("baseUrl:" + baseUrl)
var options = {
url: baseUrl
};
request(options, function (error, response, html) {
if (!error) {
console.log("no error");
}else{
console.log("else js");
console.log(error);
}
});
}
module.exports = {
request_test: request_test
};
In order to use then() you need to return a promise. So here is an example of the good old style promise chain, simply return promise from request_test and once you resolve or reject it, then() will be called:
promiseFunction().then((result) => {
console.log("complete");
});
function promiseFunction() {
return request_test();
}
function request_test() {
return new Promise(function(resolve, reject) {
setTimeout(function() {
console.log("no error");
resolve();
}, 1000);
});
}
Or maybe use the modern approach - async method to await call function that returns promise.
promiseFunction();
async function promiseFunction() {
await request_test();
console.log('complete');
}
function request_test() {
return new Promise(function(resolve, reject) {
setTimeout(function() {
console.log("no error");
resolve();
}, 1000);
});
}
Your issue is coming from var request_test = function check(baseUrl) { ... inside this function you are not returning promise, you are even returning nothing :)
if you are using async I would go ahead and use the await/async syntax. Also the package request does not return a promise, you have an alternative with request-promise-native. The promise should be the return value of your helper function. It could look like this:
var request_test = require('./request_test');
var baseUrl = "https://github.com";
var promiseFunction = async function () {
var result = await request_test.request_test(baseUrl);
console.log("complete");
}
promiseFunction();
and the module:
var request = require('request-promise-native');
var cheerio = require('cheerio');
var request_test = function check(baseUrl) {
console.log("baseUrl:" + baseUrl)
var options = {
url: baseUrl
};
return request(options).then(function (error, response, html) {
if (!error) {
console.log("no error");
} else{
console.log("else js");
console.log(error);
}
});
}
module.exports = {
request_test: request_test
};
I'm trying to wrap http.request into Promise:
new Promise(function(resolve, reject) {
var req = http.request({
host: '127.0.0.1',
port: 4000,
method: 'GET',
path: '/api/v1/service'
}, function(res) {
if (res.statusCode < 200 || res.statusCode >= 300) {
// First reject
reject(new Error('statusCode=' + res.statusCode));
return;
}
var body = [];
res.on('data', function(chunk) {
body.push(chunk);
});
res.on('end', function() {
try {
body = JSON.parse(Buffer.concat(body).toString());
} catch(e) {
reject(e);
return;
}
resolve(body);
});
});
req.on('error', function(err) {
// Second reject
reject(err);
});
req.write('test');
}).then(function(data) {
console.log(data);
}).catch(function(err) {
console.log(err);
});
If I recieve errornous statusCode from remote server it will call First reject and after a bit of time Second reject. How to make properly so it calls only single reject (I think First reject is proper one in this case)? I think I need to close res myself, but there is no close() method on ClientResponse object.
UPD:
Second reject triggers very rarely - why?
Your code is almost fine. To restate a little, you want a function that wraps http.request with this form:
function httpRequest(params, postData) {
return new Promise(function(resolve, reject) {
var req = http.request(params, function(res) {
// on bad status, reject
// on response data, cumulate it
// on end, parse and resolve
});
// on request error, reject
// if there's post data, write it to the request
// important: end the request req.end()
});
}
Notice the addition of params and postData so this can be used as a general purpose request. And notice the last line req.end() -- which must always be called -- was missing from the OP code.
Applying those couple changes to the OP code...
function httpRequest(params, postData) {
return new Promise(function(resolve, reject) {
var req = http.request(params, function(res) {
// reject on bad status
if (res.statusCode < 200 || res.statusCode >= 300) {
return reject(new Error('statusCode=' + res.statusCode));
}
// cumulate data
var body = [];
res.on('data', function(chunk) {
body.push(chunk);
});
// resolve on end
res.on('end', function() {
try {
body = JSON.parse(Buffer.concat(body).toString());
} catch(e) {
reject(e);
}
resolve(body);
});
});
// reject on request error
req.on('error', function(err) {
// This is not a "Second reject", just a different sort of failure
reject(err);
});
if (postData) {
req.write(postData);
}
// IMPORTANT
req.end();
});
}
This is untested, but it should work fine...
var params = {
host: '127.0.0.1',
port: 4000,
method: 'GET',
path: '/api/v1/service'
};
// this is a get, so there's no post data
httpRequest(params).then(function(body) {
console.log(body);
});
And these promises can be chained, too...
httpRequest(params).then(function(body) {
console.log(body);
return httpRequest(otherParams);
}).then(function(body) {
console.log(body);
// and so on
});
I know this question is old but the answer actually inspired me to write a modern version of a lightweight promisified HTTP client. Here is a new version that:
Use up to date JavaScript syntax
Validate input
Support multiple methods
Is easy to extend for HTTPS support
Will let the client decide on how to deal with response codes
Will also let the client decide on how to deal with non-JSON bodies
Code below:
function httpRequest(method, url, body = null) {
if (!['get', 'post', 'head'].includes(method)) {
throw new Error(`Invalid method: ${method}`);
}
let urlObject;
try {
urlObject = new URL(url);
} catch (error) {
throw new Error(`Invalid url ${url}`);
}
if (body && method !== 'post') {
throw new Error(`Invalid use of the body parameter while using the ${method.toUpperCase()} method.`);
}
let options = {
method: method.toUpperCase(),
hostname: urlObject.hostname,
port: urlObject.port,
path: urlObject.pathname
};
if (body) {
options.headers = {'Content-Length':Buffer.byteLength(body)};
}
return new Promise((resolve, reject) => {
const clientRequest = http.request(options, incomingMessage => {
// Response object.
let response = {
statusCode: incomingMessage.statusCode,
headers: incomingMessage.headers,
body: []
};
// Collect response body data.
incomingMessage.on('data', chunk => {
response.body.push(chunk);
});
// Resolve on end.
incomingMessage.on('end', () => {
if (response.body.length) {
response.body = response.body.join();
try {
response.body = JSON.parse(response.body);
} catch (error) {
// Silently fail if response is not JSON.
}
}
resolve(response);
});
});
// Reject on request error.
clientRequest.on('error', error => {
reject(error);
});
// Write request body if present.
if (body) {
clientRequest.write(body);
}
// Close HTTP connection.
clientRequest.end();
});
}
There are other ways as well but here you can find a simple way to make http.request as a promise or async/await type.
Here is a working sample code:
var http = require('http');
function requestAsync(name) {
return new Promise((resolve, reject) => {
var post_options = {
host: 'restcountries.eu',
port: '80',
path: `/rest/v2/name/${name}`,
method: 'GET',
headers: {
'Content-Type': 'application/json'
}
};
let post_req = http.request(post_options, (res) => {
res.setEncoding('utf8');
res.on('data', (chunk) => {
resolve(chunk);
});
res.on("error", (err) => {
reject(err);
});
});
post_req.write('test');
post_req.end();
});
}
//Calling request function
//:1- as promise
requestAsync("india").then(countryDetails => {
console.log(countryDetails);
}).catch((err) => {
console.log(err);
});
//:2- as await
let countryDetails = await requestAsync("india");
After reading all of these and a few articles, I thought I'd post a sort of "general" solution that handles both http and https:
const http = require("http");
const https = require("https");
const url_obj = require("url");
const request = async (url_string, method = "GET", postData = null) => {
const url = url_obj.parse(url_string);
const lib = url.protocol=="https:" ? https : http;
const params = {
method:method,
host:url.host,
port: url.port || url.protocol=="https:" ? 443 : 80,
path: url.path || "/"
};
return new Promise((resolve, reject) => {
const req = lib.request(params, res => {
if (res.statusCode < 200 || res.statusCode >= 300) {
return reject(new Error(`Status Code: ${res.statusCode}`));
}
const data = [];
res.on("data", chunk => {
data.push(chunk);
});
res.on("end", () => resolve(Buffer.concat(data).toString()));
});
req.on("error", reject);
if (postData) {
req.write(postData);
}
req.end();
});
}
You could use like this:
request("google.com").then(res => console.log(res)).catch(err => console.log(err))
This is heavily inspired by this article, but replaces the hacky url parsing with the built in api.
Hope this help.
const request = require('request');
async function getRequest() {
const options = {
url: 'http://example.com',
headers: {
'Authorization': 'Bearer xxx'
}
};
return new Promise((resolve, reject) => {
return request(options, (error, response, body) => {
if (!error && response.statusCode == 200) {
const json = JSON.parse(body);
return resolve(json);
} else {
return reject(error);
}
});
})
}
It's easier for you to use bluebird api, you can promisify request module and use the request function async as a promise itself, or you have the option of using the module request-promise, that makes you to not working to creating a promise but using and object that already encapsulates the module using promise, here's an example:
var rp = require('request-promise');
rp({host: '127.0.0.1',
port: 4000,
method: 'GET',
path: '/api/v1/service'})
.then(function (parsedBody) {
// GET succeeded...
})
.catch(function (err) {
// GET failed...
});