I am trying to run a NodeJS cron at a set interval using cron-job.org, but they don't have any documentation about how to actually run the script.
Basically the service visits a URL that you provide at a set interval, but I am specifically confused about what kind of code I can put on the endpoint (specifically what type of code will actually run). Can someone provide an example of what I would put at the endpoint URL?
You can do something really simple using either the HTTP module in Node.js or the popular Express module. Using express you can do something really simple like:
var express = require('express');
var app = express();
app.get("/test", function(req, res, next){
res.setHeader('Content-Type', 'application/json');
res.send(JSON.stringify({ status: 'OK', timeStamp: new Date().toISOString() }));
});
console.log('Express listening.. on 3000');
app.listen(3000);
You can really run anything you like in the /test endpoint, though when it's being called from cron-job.org they'll probably stop if you keep throwing back 400 errors at them or the script takes really long to execute.
You'd call this using the url
http://yourdomain:3000/test
And of course you might well want to change the port number and path!
cron-job.org only allows you to call an endpoint at a set time interval.
If you want to have some code run at a set interval without worrying about HTTP server, deploying, etc... Check out services like chunk.run
Here's an example code:
https://chunk.run/c/scheduled-run-example
Then you can just select the trigger "Scheduled" like so:
Related
I am curious and really willing to learn and understand the whole concept behind the request and response circle of all backend
my question is I have a node js express framework
app is started
app.use('/api',router)
require('./routers/user')(router)
require('./routers/uretim')(router)
require('./routers/durus')(router)
require('./routers/rapor')(router)```
all my functions are called and executed and waiting for a request
since the order of this app is first use
app.use('/api',router)
then the router is called at this particular point router function has nothing attached to it,
so does it mean as we started our application we have created the routes with the executed functions below the app.use
main question
user enter ..../api
our back end was hit
what is the first process, or function that happens within our backend?
So the USE is used to load middleware, what you have is to use the router middleware on the /get url..
A better example of what is happening here is to define some action middleware on that url :
app.use("/api", (req, res, next) => {
// For example, a GET request to `/api` will print "GET /api"
console.log(`${req.method} ${req.url}`);
next();
});
When you start your server, if you hit your /api url, it will log the request info in the console and continue.
However the other URL's will not.. So you can tailor specific middleware for certain endpoints.
As for your routing itself, you will need to define the routes and their controller logic. Something like :
// HTTP GET Request Definition
app.get('/api',(req, res) => {
res.send("Hey, you hit API");
} );
This will happen after the middleware has been actioned.
Express
I have a Python script that I have written that an utilizes an API to retrieve weather information, its just a simple terminal print script for right now. I am starting to learn more about HTML/JS and am wondering where I could start to learn how to pass information from my web pages to scripts.
Eventually what I am trying to work towards is passing a zip code string input from an HTML form over to my Python script on my local machine, and then have the script return data to my webpage.
The problem is, I have no idea where to start, or where even to start looking for information. For example, I understand that you can pass values to a server side application & that is kinda what I'm simulating here.
If you want to run your python script from your websites, you could use a server for that. Given that you are already into Javascript, I suggest that you create a server using a popular JS framework called Express. Express is designed for NodeJS, a JS runtime.
Once you setup your Express server, you can start creating routes and integrate them into your websites by making asynchronous calls with utilities like fetch or axios. For example, you can create a sample app like this:
var express = require('express');
var app = express();
app.get('/', function (req, res) {
res.send('Hello World!');
});
app.use('/run-script', function (req, res) {
res.send('Script run!');
};
app.listen(3000, function () {
console.log('Example app listening on port 3000!');
});
If you look closer, app.use() allows you to define routes. When a user or a JS script calls this route, the function gets executed. For example, inside the route run-script you could execute yours:
app.use('/run-script', function(){
const spawn = require("child_process").spawn;
const pythonProcess = spawn('python',["path/to/script.py", arg1, arg2, ...]);
});
As you see, there are numerous possibilities. For more info on calling python scripts from node, see this stackoverflow question.
You could start digging into NodeJS in general. For that, a good place to start is the official guides.
Please let me know if this answer was useful to you.
Is it possible to use console.log() in the backend (I am using express) to output things in the frontend.
for example:
const express = require('express');
const app = express();
client.console.log('Hi');
How would I do it?
Thanks.
There is no built-in support for a server to cause something to show in the client console. I'm not sure what the actual use case for that is since the console is typically a debugging aid, not an actual end-user thing.
In any case, if you want to do that, you would have to have cooperating code on both the client and the server and then how that code works depends upon the context in which you want to put the info in the console.
From a page load
From a page load, the server could embed a small script in the page that would output into the browser console when the page loads and runs.
From an Ajax call
Here, you could include a property in some returned JSON that contains the desired console message and then the client code making the ajax call would have to grab that property and call console.log() with it.
From any random time on the server
If you're not in the context of an existing request from the browser or web page Javascript (as in the previous two points), then you would need some push channel connected between the web page and the server such as a webSocket connection, a socket.io connection or a SSE connection. Then, you could send a message to the client and the client would need some code listening for those incoming messages and then display them in the local console upon receiving them.
try it:
The 'send' method of 'res' object of Express, is one of so many ways to send a response to client in the request event.
const express = require('express')
const app = express()
app.get('/test', (req, res) => {
return res.send('Hello world!')
})
There is no support as jfriend00 said, but there is a way to go around this.
So lets say the user requests /test
You want to displayin his console Hello World
So you do:
const express = require('express')
const app = express()
app.get('/test', (req, res) => {
return res.send('<script>console.log(Hello world!)</script>')
})
And that acts as a full client console log. There ya go. (Single Time)
Or setup socket.io as jfriend said in his post if you want to constantly post console messages (multiple times).
Having this simple express app example:
var express = require('express')
var app = express()
app.use(express.static(__dirname+'/public'))
app.get('/', function(request,response) {
response.send("This wont matter if we got an index.hml after all")
})
app.listen(2311, function() {
console.log("app escuchando en Maricela DDMM")
})
And at /public I got an index.html.
When I get rid of such html the string in the send() method will be sent, received and rendered at browser.
What does actually happen with the response.send() string talking about the HTTP response, as the HTML is which is send and so rendered at browser?
Express goes through the chain of middleware in the order in which it was added. You have added express.static as the first middleware, so it will be ran first.
In the event express.static cannot find a file, it calls next(), allowing the next bit of middleware to run. This is your handler set up with app.get('/' //..., which sends the data as you have told it to.
I think it basically sets up the header information based on the parameter in send and then send the http response
I want to allow an authenticated client in Express to access to other web applications that are running on the server, but on different ports.
For example, I have express running on http://myDomain and I have another application running on say port 9000. I want to be able to reach the other app through http://myDomain/proxy/9000.
I had a little bit of success using node-http-proxy, for example:
function(req, res) {
var stripped = req.url.split('/proxy')[1];
var path = stripped.split('/');
var port = path.shift();
var url = path.join('/');
req.url = url;
proxy.web(req, res, {
target: 'http://127.0.0.1:' + port
});
}
However, the big problem is that when the web app makes GET requests, such as for /js/lib.js, it resolves to http://myDomain/js/lib.js, which is problematic because express is not aware of those assets. The correct request would be to http://myDomain/proxy/9000/js/lib.js. How do I route all these additional requests?
What you need to do is to replace URLs in the initial page with the new URL pattern. What is happening is that the initial page that your reverse proxy returns has a reference to:
/js/lib.js or http://myDomain/js/lib.js
so when the browser makes a second request it has the wrong pattern for your reverse proxy.
Based on the incoming request you know what the pattern should look like. In your example it's http://myDomain/proxy/9000. You then fetch the appropriate page from the other server running on http://127.0.0.1:9000/. You do a string replace on any resources in that file. You'll need to experiment with the pattern but you might look for 'script src="/' or 'href="/' and you might find regex helps with the pattern if, for example, the src attribute isn't the first listed in a script tag.
For example you might find 'scr="/' and then you replace it with 'src="/proxy/9000/' that way when the browser asks for that local resource it will come through with the port that you're looking for. This is going to need experimentation and it's a great algorithm to write unit testing around to get perfect.
Once you've done the replacement you just stream that page to the client. res.send() will do this for you.
Something else that you might find useful is that ExpressJS gives you a way to pull out the port number with a little less hassle than you're doing. Take a look at this example:
app.get('/proxy/:port', function(req, res){
console.log('port is ' + req.params.port);
});
I don't think http://myDomain/proxy/9000 is the correct way to do it. Web pages are going to assume the site's domain to be just myDomain and not myDomain/proxy/9000, because that is what the standard says.
Your use case would be better served by using subdomains like 9000.proxy.myDomain.