I'm a beginner at node js and I'm doing a simple project with pure node.js.
So here is my code:
if(req.url ==="/"&&req.method==="POST"){
let reqBody = "";
req.on('data', chunk=>{
reqBody += chunk.toString();
});
req.on("end", ()=>{
reqBody = reqBody.split("&");
for(let i=0; i<reqBody.length; i++){
reqBody[i]=reqBody[i].split("=");
reqBody[i] = reqBody[i][1];
};
//filter country
let countryFound;
if(reqBody[1].length>0){
let countryList = "";
let countryVal = [];
countryListStream = fs.createReadStream("./public/country.list.json", "UTF-8");
countryListStream.on("data", countryChunk=>{
countryList+=countryChunk;
countryChunk = JSON.parse(countryChunk);
countryFound = countryChunk.filter(elem=> elem["name"].toLowerCase()==reqBody[1].toLowerCase());
if(countryFound.length!==0){
countryListStream.destroy();
};
});
countryListStream.on("end", ()=>{
countryFound = "Not Found"
});
};
});
};
My problem is below "filter country" comment:
when I log the "countryFound" variable outside of the events of "countryListStream", it displays undefined.But when i log it inside of the events, it displays what I want. I think it's becaus of how node.js is made, but I don't know to continue my code if it's undefined.
I think that I need to include a code that waits until the variable is updated, and then it runs the rest.
I tried with this after the if statement, and it didn't fixed it:
if(countryFound!===undefined){
console.log(countryFound);
}
From looking at the documentation, calling countryStream.destroy() emits close and error events. So, it would make sense to add a handler to the close event where you can continue processing the values that you have assigned to those variables:
countryStream.on('close', () => {
console.log(countryFound) // should not be undefined now
// ...do something with your new values
});
Related
Little info, i have an arp.js file which takes a subnet address "192.168.2" and gets all strings returned from arp -a and stores in an array.
I can't figure out why my arpList function is returning an undefined value in my index.js file.
All the console.logs are returning the correct values in the arp.js page when called from the index.js, but the ipObj is coming up undefined. Even the console.log before i return of ipObj works.
Any help would be greatly appreciated.
var { spawn } = require('child_process');
const arpLs = spawn('arp', ['-a']);
var bufferData;
module.exports = {
arpList: function (subnet) {
arpLs.stdout.on('data', data => {
bufferData += data
})
arpLs.stderr.on('data', data => {
console.log('error: ' + data);
});
arpLs.on('exit', function (code) {
if (code != 0) {
console.log("Error exiting"); //if error occurs
}
console.log("exit start 1"); // checking internal processes at stages
var dataArray = bufferData.split(' ');
var ipArray = [];
for (i = 0; i < dataArray.length; i++) {
if (dataArray[i].includes(subnet)) {
ipArray.push(dataArray[i]);
console.log("loop working");
}
}
var ipObj = { "lanIps": ipArray };
console.log("Object is there: "+ipObj)
return ipObj; // this obj should be returned to the index.js call using
})
},
sayMyName: function () {
return "Hello";
}
}
//arpList(ipSubnet);
//INDEX.js
//the index page looks like this
//var arp = require('./arp.js);
//var ipSubnet = "192.168.2";
//var lanIps = arp.arpList(ipSubnet);
//console.log(lanIps);
I ended up adding a callback function to arpList - function (subnet, callback)
Then instead of returning the value pass it into the callback
Then on the index.js side instead of
var lanIps = arp.arpList(value)
i used
arp.arpList(value, function(res){lanIps = res}
return ipObj; // this obj should be returned to the index.js call using
It won't be returned. The reference say nothing about return value. Node-style callbacks rarely work like that because they are potentially asynchronous and returned value cannot be taken into account.
This a special case of this well-known problem. The process is asynchronous and is finished after arp.arpList(ipSubnet) call, there's nothing to assign to lanIps. This is a use case for promises. There are already third-party promisified counterparts like child-process-promise.
The problem can be also solved by moving to synchronous API. child_process functions have synchronous counterparts, including spawnSync.
I am a total scrub with the node http module and having some trouble.
The ultimate goal here is to take a huge list of urls, figure out which are valid and then scrape those pages for certain data. So step one is figuring out if a URL is valid and this simple exercise is baffling me.
say we have an array allURLs:
["www.yahoo.com", "www.stackoverflow.com", "www.sdfhksdjfksjdhg.net"]
The goal is to iterate this array, make a get request to each and if a response comes in, add the link to a list of workingURLs (for now just another array), else it goes to a list brokenURLs.
var workingURLs = [];
var brokenURLs = [];
for (var i = 0; i < allURLs.length; i++) {
var url = allURLs[i];
var req = http.get(url, function (res) {
if (res) {
workingURLs.push(?????); // How to derive URL from response?
}
});
req.on('error', function (e) {
brokenURLs.push(e.host);
});
}
what I don't know is how to properly obtain the url from the request/ response object itself, or really how to structure this kind of async code - because again, I am a nodejs scrub :(
For most websites using res.headers.location works, but there are times when the headers do not have this property and that will cause problems for me later on. Also I've tried console logging the response object itself and that was a messy and fruitless endeavor
I have tried pushing the url variable to workingURLs, but by the time any response comes back that would trigger the push, the for loop is already over and url is forever pointing to the final element of the allURLs array.
Thanks to anyone who can help
You need to closure url value to have access to it and protect it from changes on next loop iteration.
For example:
(function(url){
// use url here
})(allUrls[i]);
Most simple solution for this is use forEach instead of for.
allURLs.forEach(function(url){
//....
});
Promisified solution allows you to get a moment when work is done:
var http = require('http');
var allURLs = [
"http://www.yahoo.com/",
"http://www.stackoverflow.com/",
"http://www.sdfhksdjfksjdhg.net/"
];
var workingURLs = [];
var brokenURLs = [];
var promises = allURLs.map(url => validateUrl(url)
.then(res => (res?workingURLs:brokenURLs).push(url)));
Promise.all(promises).then(() => {
console.log(workingURLs, brokenURLs);
});
// ----
function validateUrl(url) {
return new Promise((ok, fail) => {
http.get(url, res => return ok(res.statusCode == 200))
.on('error', e => ok(false));
});
}
// Prevent nodejs from exit, don't need if any server listen.
var t = setTimeout(() => { console.log('Time is over'); }, 1000).ref();
You can use something like this (Not tested):
const arr = ["", "/a", "", ""];
Promise.all(arr.map(fetch)
.then(responses=>responses.filter(res=> res.ok).map(res=>res.url))
.then(workingUrls=>{
console.log(workingUrls);
console.log(arr.filter(url=> workingUrls.indexOf(url) == -1 ))
});
EDITED
Working fiddle (Note that you can't do request to another site in the browser because of Cross domain).
UPDATED with #vp_arth suggestions
const arr = ["/", "/a", "/", "/"];
let working=[], notWorking=[],
find = url=> fetch(url)
.then(res=> res.ok ?
working.push(res.url) && res : notWorking.push(res.url) && res);
Promise.all(arr.map(find))
.then(responses=>{
console.log('woking', working, 'notWorking', notWorking);
/* Do whatever with the responses if needed */
});
Fiddle
Or quite possibly I am doing it wrong, in fact, more than likely I am doing it wrong.
Have a table which contains a "tree" of skill, starting at the root level and may be as deep as ten levels (only two so far), but I want to return it as one big fat JSON structure, so I want to ask the database for each set of data, build my structure then ask for the next level.
Of course if I just send of my requests using mongoose, they will come back at any time, as they are all nice asyncronous calls. Normally a good things.
Looking at the documentation for Mongoose(using 4.1.1) it seems like it has a promise built in, but whenever I try to use it the api call throws a hissy fit and I get a 500 back.
Here is my simple function:
exports.getSkills = function(req,res) {
console.log("Will return tree of all skills");
for (var i = 0; i<10; i++){
var returnData = [];
console.log("Lets get level " + i );
var query = Skill.find({level: i });//The query function
var promise = query.exec; //The promise?
promise.then(function(doc) { //Totally blows up at this point
console.log("Something came back")
return "OK";
});
}
}
The Mongoose documentation on the subject can be found here
http://mongoosejs.com/docs/api.html#promise_Promise
var promise = query.exec;
// =>
var promise = query.exec()
exports.getSkills = function(req,res) {
console.log("Will return tree of all skills");
var p;
for (var i = 0; i < 10; i ++) {
if (i == 0 ) {
p = Skill.find({level:i}).exec();
} else {
p.then(function (){
return Skill.find({level:i}).exec()
})
}
p.then(function (data) {
//deal with your data
})
}
p.then(function () {
// deal with response
})
}
I have been trying to retrieve the data using the MongoJS driver for node.js.The Code which I am using is as follows
req.on('end', function(){
var decodedBody = querystring.parse(fullBody);
story=decodedBody.name;
var z=new Array();
console.log(story);
res.writeHead(200,{'Content-Type': 'text/html'});
res.write('<html><body>');
db.frames.find({str_id:story}).toArray(function(err,doc){
console.log(doc);
for(var t=0;t<doc.length;t++)
{
var picid=doc[t].pic_id;
console.log(picid);
db.pictures.find({_id:picid}).toArray(function(err,pic){
res.write('<img src="'+pic[0].name+'"/>');
});
}
})
res.end('</body></html>');
});
The problem here is that because of the asynchronous nature of the code the response gets ends first and then the code inside the block of database gets executed and because of that nothing gets displayed on the browser i.e an image in this case .Thankx in advance.
Don't fight the asynchronous nature of node.js, embrace it!
So you should fire off all your requests, marking each one as completed when the response arrives. When all requests are completed, render your images and body/html closing tags.
I don't usually work with node.js, so I can make some mistakes, but it may look like this:
res.write('<html><body>');
db.frames.find({str_id:story}).toArray(function(err,doc){
console.log(doc);
var completed = {};
for(var t = 0; t < doc.length; t++) {
var picid = doc[t].pic_id;
completed.picid = false;
console.log(picid);
db.pictures.find({_id: picid}).toArray(function(err, pic) {
// mark request as completed
completed.picid = pic;
// check if all requests completed
var all_finished = true;
for(var k in completed) {
if(completed[k] === false) {
all_finished = false;
break;
}
}
// render final markup
if(all_finished) {
for(var k in completed) {
var pic = completed[k];
res.write('<img src="'+pic[0].name+'"/>');
}
res.end('</body></html>);
}
});
}
})
just put the res.end('</body></html>'); inside your db.frames.find function. Check when you reached doc.length - 1 and then send the end command.
I'm having some issues using Node.js as a http client against an existing long polling server. I'm using 'http' and 'events' as requires.
I've created a wrapper object that contains the logic for handling the http.clientrequest. Here's a simplified version of the code. It works exactly as expected. When I call EndMe it aborts the request as anticipated.
var http = require('http');
var events = require('events');
function lpTest(urlHost,urlPath){
this.options = {
host: urlHost,
port: 80,
path: urlPath,
method: 'GET'
};
var req = {};
events.EventEmitter.call(this);
}
lpTest.super_ = events.EventEmitter;
lpTest.prototype = Object.create(events.EventEmitter.prototype, {
constructor: {
value: lpTest,
enumerable: false
}
});
lpTest.prototype.getData = function getData(){
this.req = http.request(this.options, function(res){
var httpData = "";
res.on('data', function(chunk){
httpData += chunk;
});
res.on('end', function(){
this.emit('res_complete', httpData);
}
};
}
lpTest.prototype.EndMe = function EndMe(){
this.req.abort();
}
module.exports = lpTest;
Now I want to create a bunch of these objects and use them to long poll a bunch of URL's. So I create an object to contain them all, generate each object individually, initiate it, then store it in my containing object. This works a treat, all of the stored long-polling objects fire events and return the data as expected.
var lpObject = require('./lpTest.js');
var objWatchers = {};
function DoSomething(hostURL, hostPath){
var tempLP = new lpObject(hostURL,hostPath);
tempLP.on('res_complete', function(httpData){
console.log(httpData);
this.getData();
});
objWatchers[hosturl + hostPath] = tempLP;
}
DoSomething('firsturl.com','firstpath');
DoSomething('secondurl.com','secondpath);
objWatchers['firsturl.com' + 'firstpath'].getData();
objWatchers['secondurl.com' + 'secondpath'].getData();
Now here's where it fails... I want to be able to stop a long-polling object while leaving the rest going. So naturally I try adding:
objWatchers['firsturl.com' + 'firstpath'].EndMe();
But this causes the entire node execution to cease and return me to the command line. All of the remaining long-polling objects, that are happily doing what they're supposed to do, suddenly stop.
Any ideas?
Could it have something to do with the fact that you are only calling getData() when the data is being returned?
Fixed code:
function DoSomething(hostURL, hostPath){
var tempLP = new lpObject(hostURL,hostPath);
tempLP.on('res_complete', function(httpData){
console.log(httpData);
});
tempLP.getData();
objWatchers[hosturl + hostPath] = tempLP;
}
I have seemingly solved this, although I'm note entirely happy with how it works:
var timeout = setTimeout(function(){
objWatchers['firsturl.com' + 'firstpath'].EndMe();
}, 100);
By calling the closing function on the object after a delay I seem to be able to preserve the program execution. Not exactly ideal, but I'll take it! If anyone can offer a better method please feel free to let me know :)