如何在Node JS中同步'http请求'

Question

I'm trying to execute 3 'http requests'. The problem is, because of the nature of asynchronous mode, it doesn't execute in order. All requests are to internal apis. Here's the sample code :-

setInterval(function () {
  // First request
  request({}, function (error, response, body) {
   // Second request
   request({}, function (error, response, body) {
    // Third request
    request({}, function (error, response, body) {
    })
   })
  })
},1000);

What i'm trying to achieve is get data based on one condition ( First request ), update data ( Second request ) and send sms and emails ( Third request ). Because of the asynchronous nature, code is getting repeated many times. I'm using setInterval so the code will always run every second

Answer 1

You can easily sequence requests using Promises

// Load Dependencies: 
var Promise = require('promise');
var request = require('request');

// Begin Execution:
main();

function main() {
  getData()                //Executes 1st
   .then(updateData)       //Whatever is 'fulfilled' in the previous method, gets passed to this function updateData
   .then(sendNotification) //Whatever is fulfilled in the previoud method, gets passed to this function sendNotification.
   .catch(function(err) {
     console.log('If reject is called, this will catch it - ' +err);
   });
}

// Request #1:
function getData() {
  return new Promise(function(fulfill, reject) {
    request({}, function(err, res, body) {
      if (err) {
        reject('Error making request - ' +err);
      } else if (res.statusCode !== 200) {
        reject('Invalid API response - ' +body);
      } else {
        fulfill(body);
      }
    });
  });
}

// Request #2:
function updateData(data) {
  return new Promise(function(fulfill, reject) {
    request({}, function(err, res, body) {
      if (err) {
        reject('Error making request - ' +err);
      } else if (res.statusCode !== 200) {
        reject('Invalid API response - ' +body);
      } else {
        fulfill(body);
      }
    });
  });
}


// Request #3
function sendNotification(phoneNumber, email) {
  return new Promise(function(fulfill, reject) {
    request({}, function(err, res, body) {
      if (err) {
        reject('Error making request - ' +err);
      } else if (res.statusCode !== 200) {
        reject('Invalid API response - ' +body);
      } else {
        fulfill(body);
      }
    });
  });
}

So basically just wrap your async functions with return new Promise , to return the ready data via fulfill or reject . In function main() , you can see how the sequence for this order has been easily defined.

Answer 2

Answer to title: You can't make them synchronous. But you can sequence them.

You likely should replace the setInterval with a setTimeout and then issue another setTimeout after the third request completes. Otherwise the setInterval will cause the first request re-issued before the third request has an opportunity to complete. Which is likely the issue.