Really fast, this question may have already been asked, but I am not totally clear on the terminology and have had no success when searching for a solution.
I am attempting to create a simple web application that can receive get and post requests. Then, I would like to take the information I receive from these requests and use them in a javascript file embedded in html that is displayed. I think it may be more clear with code. This is my app.js:
var express = require('express');
var app = express();
var assert = require('assert');
app.use(express.static('javascript'));
app.get('/', function(req, res) {
res.render('index.jade');
});
app.listen(3000);
I would then like to be able to take information received from a get or post request, specifically in JSON format, and then be able to use it in javascript that I have linked to index.jade. To make matters slightly more confusing in index.jade the only line is:
include map.html
So ideally I would be able to get the information to javascript in that html file.
I want to be able to pretty continuously update map.html using javascript based on frequent get and post commands.
This could be a very simple solution, I am pretty new with web application programming in general, and I have been struggling with this problem. Thanks in advance, and ask if you need any clarification.
I think you need to understand what you are doing. You are creating a web server using node.js. Express framework simplifies that for you. The official documentation of express is pretty great. You should refer that especially this link.
Now, in your application, you need to create endpoints for GET and POST requests. You have already created one endpoint "/" (root location) that loads your home page which is the contents of the file index.jade. A small example is :
app.get('/json', function (req, res) {
res.setHeader('Content-Type', 'application/json');
res.send(JSON.stringify({ a: 1 }));
});
Jade is a templating engine which resolves to HTML. You should refer its documentation as well. Since as you said, you are not very familiar with these, you could simply use HTML as well.
After this tasks are quite simple. In your javascript, using ajax calls you can access the GET or POST endpoints of your server and do the desired actions.
Hope it helps!
The way I get it you want to be able to call an endpoint (lets assume /awesome) pass some info and then write to a Javascript file that you can then reference in your html.
Something like the below would write a main.js file in your public folder. You can make it write whatever you want.
var fs = require('fs');
fs.writeFile("/public/main.js", "console.log('Hello!')", function(err) {
if(err) {
return console.log(err);
}
console.log("The file was saved!");
});
You can then reference /public/main.js in your html.
Check that: Writing files in Node.js
If I misunderstood your intentions, apologies. :)
So you want to reviece continuously data from the server maybe web sockts are an option for you http://socket.io/docs/
This way u will open a stable connection from the client to the server. This is a great way if u want to get updates done by other clients.
If you want to trigger the changes by the client then ajaxs calls(http://www.w3schools.com/ajax/) as hkasera mentioned are the way to go.
Related
My main function is I am creating a link-shortening app. When someone entered a long URL, it will give a short URL. If the user clicked on the short link it will search for the long URL on the DB and redirect it to the long URL.
Meantime I want to get the click count and clicked user's OS.
I am currently using current code :
app.get('/:shortUrl', async (req, res) => {
const shortUrl = await ShortUrl.findOne({short: req.params.shortUrl})
if (shortUrl == null) return res.sendStatus(404)
res.redirect(shortUrl.full)
})
findOne is finding the Long URL on the database using ShortID. I used mongoDB here
My questions are :
Are there multiple redirect methods in JS?
Is this method work if there is a high load?
Any other methods I can use to achieve the same result?
What other facts that matter on redirect time
What is 'No Redirection Tracking'?
This is a really long question, Thanks to those who invested their time in this.
Your code is ok, the only limitation is where you run it and mongodb.
I have created apps that are analytics tracker, handling billion rows per day.
I suggest you run your node code using AWS Beanstalk APP. It has low latency and scales on your needs.
And you need to put redis between your request and mongodb, you will call mongodb only if your data is not yet in redis. Mongodb has more read limitations than a straight redis instance.
Are there multiple redirect methods in JS?
First off, there are no redirect methods in Javascript. res.redirect() is a feature of the Express http framework that runs in nodejs. This is the only method built into Express, though all a redirect response consists of is a 3xx (often 302) http response status and setting the Location header to the redirect location. You can manually code that just as well as you can use res.redirect() in Express.
You can look at the res.redirect() code in Express here.
The main things it does are set the location header with this:
this.location(address)
And set the http status (which defaults to 302) with this:
this.statusCode = status;
Then, the rest of the code has to do with handling variable arguments, handling an older design for the API and sending a body in either plain text or html (neither of which is required).
Is this method work if there is a high load?
res.redirect() works just fine at a high load. The bottleneck in your code is probably this line of code:
const shortUrl = await ShortUrl.findOne({short: req.params.shortUrl})
And, how high a scale that goes to depends upon a whole bunch of things about your database, configuration, hardware, setup, etc... You should probably just test how many request/sec of this kind your current database can handle.
Any other methods I can use to achieve the same result?
Sure there are. But, you will have to use some data store to look up the shortUrl to find the long url and you will have to create a 302 response somehow. As said earlier, the scale you can achieve will depend entirely upon your database.
What other facts that matter on redirect time
This is pretty much covered above (hint, its all about the database).
What is 'No Redirection Tracking'?
You can read about it here on MDN.
I'm doing project in nodejs and html .can anybody help how to set value to text field in html from server.js. For example I've text field with id 'name' on index.html. i use res.body.name = 'nametest' .but its not working .please give me a simple example . Thank you friends
In order to set a field from the server, you want to make it a preset value which you define when sending the HTML or you want to set it dynamically later on. The first option is easy, the second one a bit advanced.
Let's look at option 1. This is just a very basic example! Please don't use this in production.
index.html
<!DOCTYPE html>
<html>
<head><!-- your stuff here --></head>
<body><input type="text" name="someVal" value="{{someVal}}"></body>
</html>
This might be your HTML. Just but a distinctive placeholder where you want your value to go. There might be better techniques out there to do this, but for the sake of simplicity I chose this way.
server.js
var http = require('http');
var fs = require('fs');
http.createServer((req, res) => {
fs.readFile('index.html', (err, data) => {
if (err) {
res.writeHead(500);
res.end(err);
return;
}
data = data.toString().replace(/\{\{someVal\}\}/, 'your value here');
res.writeHead(200);
res.end(data, 'utf8');
});
}).listen(8080);
This server.js will open a HTTP server on port 8080. It will try to read index.html from the same directory. If it fails, it will send the error message to the client, else it will replace your placeholder in your HTML with your value and then send the modified content to the client.
If that's all you want to do, PHP might do a better job for you (but that's just my 2 cents :) )
Option 2 is a lot more elaborate. You would have to either use AJAJ (Asynchronous Javascript and JSON) which requires the client to know when to fetch the value or you could make use of websockets which enable the server to push a value to the client. For either of those there are a lot of tutorials out there which are a lot more detailed than anything I could put together for you here.
If you want to use those techniques, but are a bit unsure about their iomplementation, you might want to look at frameworks like Meteor and Socket.IO
You can't set a client-side thing from the server-side. They're absolutely different physical layers.
What you need is AJAX to request a resource from your Web app to your NodeJS server-side app, and set what you put in you response to the whole text field.
Maybe you'll need to take a look at ExpressJS to build a simple RESTful service to share resources between your client and server tiers.
Let me preface by saying that I have spent a considerable amount of time trying to figure out the solution to this problem but I have not discovered something that works. I am using node and want to share a variable between my app.js server file and a client side javascript file (demo.js).
I run node app.js to launch the server and demo.js runs in the client. I have tried using module.exports and export but when I try importing in the demo.js file or referring to the module.exports var I get errors. Maybe I'm approaching this is in the wrong way.
For example, I am trying to use the node wikipedia package to scrape data. I have the following in my app.js file:
var wikipedia = require('node-wikipedia');
wikipedia.page.data('Clifford_Brown', { content: true }, function(response) {
console.log(response);
export const response = response;
module.exports.data = response
});
In my demo.js file I have tried importing this response var and using the module.exports var but I have been unsuccessful.
Anyone have any solutions to this issue or different approaches I should take?
Browser javascript files run in the browser. node.js javascript files run on the server. You cannot directly export things from one to the other. They are on completely different computers in different locations.
It is very important for developers to understand the notion that server-side code runs on the server and client-side code runs on the browser. The two cannot directly call each other or reach the other's variables. Imagine your server is in a data center in Seattle and the browser is running on a computer in Venice.
See How to access session variables in the browser for your various choices described for a previous answer.
In a nutshell, you can have the server insert a javascript variable into the generated web page so that when the javascript runs in the web page on the browser, it can then access that variable in its own page. Or, you can create an Ajax call so the client can request data directly from the server. Or you can have the server put some data in a cookie which the Javascript in the browser can then access.
If the data is easily known by the server at the time the page is generated and you are using some sort of page template system, then it is very easy to just add a <script> tag to the generated page that defines one or more Javascript variables that contain the desired information. Then, the client-side Javascript can just refer to those variables to have access to the data.
To pass data in http there is a request message and response message and the data needs to be inside that message.
In the request you can either pass variables in the request URL
http://host_name/path?key=value
Or inside the request body or headers.
In the response you pass back variables in the response header or response body
First Example:
One way of processing a URL request from the browser explicitly while passing variables is to set up your server to render a html page with those variables embedded.
If you use a templating engine like jade, you can consume the sent variables directly into the template using res.render({ key: 'value' }) rather than using a promise based api call which would run when the user performs some action on the client.
For instance.
// SERVER setup rendering engine
app.get('/', function(req, res) {
res.render( 'index', { key: 'value' })
}
Which will render index.html to the client with the key-value pair passed to the template file used to serve up the index.html (for example jade or ejs).
Second Example:
Using axios you can set up an action to call a server api (you can also pass variables in the URL, headers or body). Using the promise pattern you can then use these variables after the server api has responded.
// CLIENT setup axios
axios.get(URL + '/getkeyvalue')
.then(function(response) {
const value = response.data.key
})
On you server using express you (this is where you would get the optional request variables mentioned above) send back response variables in the body like this.
// SERVER setup express
app.get('/getkeyvalue', function(req, res) {
res.send({ key: 'value' })
}
Note that these are simple examples.
They are too completely different systems. The best way to accomplish what you're trying to do is the create a variable in your html on the server side by stringifying your data
<script> var my_data = <%= JSON.stringify(data) %> </script>
Thats an example using ejs, a common templating language in expressjs
I need to develop a web app for admin panel using node.js.I just learnt how to display a static html using node.js.
var sys = require("sys"),
my_http = require("http");
fs = require('fs');
my_http.createServer(function(request,response){
fs.readFile("index.html",function(err,data){
if(err){
console.log("error occured");
}
response.writeHead(200, {'Content-Type': 'text/html','Content- Length':data.length});
response.write(data);
response.end();
});
}).listen(7777);
sys.puts("Server Running on 7777");
But I am not able to understand how to change the view from one html page to another, like when the login button is clicked. I've used to php earlier where I give the name of the php file in the action of the form. Similarly what should be done in node.js?
First of all,
For node.js, everything from routing to redirection is to be hand-coded. You need to learn more in node.js for this. You can refer - http://www.nodebeginner.org/ site for learning.
Also if you want to use some high level library , you can go through - expressjs - http://expressjs.com/starter/basic-routing.html and may google for node express applications.
For you question -
You have to extract information from req.url property and then branch your code accordingly for file reading.
More of this can be found in
http://nodejs.org/api/http.html#http_message_url
Hope it will help you.
I'm developing extension to an existing app using expressjs. By requirements I need to do server side rendering. Our API server is running on JAVA.
In my express app, I'm going to have to render page while making serverside calls to JAVA server. For example, I'm going to call getCategories, getVendors, getReviews etc APIs in order get data that I need to pass to rendering template.
What is a good way to accomplish this? I mean pack all of that into a single object and pass to res.render() method. Could you please provide me with some basic examples? I imagine that I would need to create a module that does all of this and returns some nice object...
All of the examples on the internet show something like res.render('index', { data: 'someData'}), however in this case data is bootstrapped. I would need a data to be compiled with several API calls and then passed to the rendering method.
Thanks!
It really depends on whether you want to call your Java API server side or client side.
If server side, your express route containing res.render() will need to collect all the information it needs from Java before rendering the page. If your API is slow, the page load will be slow. If possible, use something like async.parallel to avoid blocking.
Your code sample is correct. res.render('index', { foo: 'bar'})
This would add the foo variable to the root scope of your view. How you build up the data structure is entirely up to you. I would recommend using async.parallel and/or async.series to collate all of the data. If they are all completely independent, run them in parallel.
// an example of how to run each in parallel and then render the view.
var getCategories = function(done) {
// get something
done();
};
var data = {};
async.parallel([
getCategories, // <-- adds to the data structure
getVendors,
getReviews
], function(err) {
res.render('index', { data: data });
});
Your other option is using express to render the base page and using something like jQuery to hit the Java API and update the relevant page fragments.