I am relatively new to node (moving from PHP) and am encountering a problem that took me a while to figure out (meaning it took me a while to figure out what the problem was and now I have no idea how to fix it).
At the top of my node app (server.js), I have some requires. One of this requires my homemade api like this:
const express = require('express');
const app = express();
const v1 = require('./app/v1.js');
The v1 is just a function that returns the output to the api. However, there are many code problems with the v1 api as I have just wrote it and am testing it for the first time.
However, whenever there is a problem with the v1 function, node doesn't print it out and stop the program like it would if the problem were in the main server.js file. In fact (I am using nodemon so I don't have to restart each time), node just continues running like everything is moving perfectly smoothly. I understand why node would want to do this (they want people's app's to not be dependent on the quality of code of the module). However, this is not helpful for me as I have no idea where my problem is in the v1 module.
Does anyone know how to turn on errors/exceptions for modules? Any help appreciated.
Sounds like its doing its job just fine. Are you sure your v1 is returning the right value? or printing out the value that v1 is returning in server.js? because its not going to automatically print out the returned value, you still have to put it in a console.log(v1()); or something similar. without knowing what v1 actually returns, its hard to say what is suppose to be printed.
Related
Hi I am structuring my Node.js project based on this, like so:
Root
product name
index.js: (contains requires for the product and the main export)
productName.js: contains application logic
test
test1.js
test2.js
...
Now I have two questions
What should logically go in index.js? At the moment I have this (would this be a good way to do things and what else might I include in index.js?):
// index.js
var myServer = require('./myServer.js'); // "product name" = "myServer"
module.exports = {
run: myServer.listen
}
Does it matter what I call the object key in module.exports (currently "run")? Why does the server always run when I execute index.js with $ node index.js how does it automatically know to run myServer.listen?
P.S.: I am aware of web structure auto-generation tools, I just wish to understand the logical reason for this suggested structure (the idea of not having any logic in index.js)
As you mentioned this is a Express service, if it is only handling backend of some application or more specifically this is only backend application, I would suggest you change name of your index.js to server.js(Thus explicitly stating that it'll process all service requests).
But if not then even index.js is fine.
Now for
1
What you've put is absolutely fine, apart from this you could require all modules, routes(or controllers whatever you name them) in a way that it serves as entry point to your application. Try not to put any logic in here.
2
Actually the server runs because it executes the script in the file called index.js, the script says myServer.listen, now if you had written console.log("Hello World") and used $ node index.js it would've printed Hello World instead.
Node just expects and executes script that is there in index.js, in your case it is to start the server.
About the logic that why not put anything else in index.js, for me the reasoning I consider good enough is it provides abstraction as it is the entry point I don't want index.js to worry about things like what to do with this data and all. I believe it should provide a base to setup server. Thus following single responsibility to some extent. Also I won't have to touch it ever in projects lifetime unless some major change occurs e.g. I decide to shift from express to something else.
EDIT
Why have a key called run
You seem to have answered it yourself(in comments), you are giving or more proper description would be you're attaching an object to module.exports as it is a object similar to JSON it was supposed to have a key(which could be anything not necessarily run it could've been hii). Now if you don't want to pass a key and export only one thing that is server.listen then you could write same as module.exports = myServer.listen; instead of
module.exports = {
hii: myServer.listen
}
Note that you could export more modules using the way you did. For more details about module.exports refer this or better google about it as this link might expire anytime and does not seem an ideal thing to put on SO.
I'm trying to create selenium tests that run each step synchronously, without using .then(), or async/await. The reason for this is that I want to create a set of functions that allow pretty much anyone on our test team, almost regardless of tech skills to write easy to read automated tests. It looks to me like webdriver-sync should give me exactly what I want. However, the following dummy code is producing problems:
var wd = require('webdriver-sync');
var By = wd.By;
var Chromedriver = wd.Chromedriver;
var driver = new Chromedriver;
driver.get('https://my.test.url');
var myButton = driver.findElement(By.cssSelector('[id*=CLICK_ME]'));
myButton.click();
It tries to run - browser is launched, and page starts to load... but the steps are not executed synchronously - it goes on and tries to find and click "myButton" before the page has finished loading, throwing a "no such element" error... which to me kinda defeats the point of webdriver-sync?! Can someone tell me where I am going wrong?
FWIW, I have webdriver-sync 1.0.0, node v7.10.0, java 1.8.0_74, all running on CentOS 7.
Thanks in advance!
You need to put double-quotes around "CLICK_ME" as it's a string value.
Generally, though, it's a good idea to Wait for specific elements because dynamic pages are often "ready" before all their elements have been created.
One of the pleasures of frameworks like Rails is being able to interact with models on the command line. Being very new to node.js, I often find myself pasting chunks of app code into the REPL to play with objects. It's dirty.
Is there a magic bullet that more experienced node developers use to get access to their app specific stuff from within the node prompt? Would a solution be to package up the whole app, or parts of the app, into modules to be require()d? I'm still living in one-big-ol'-file land, so pulling everything out is, while inevitable, a little daunting.
Thanks in advance for any helpful hints you can offer!
One-big-ol'-file land is actually a good place to be in for what you want to do. Nodejs can also require it's REPL in the code itself, which will save you copy and pasting.
Here is a simple example from one of my projects. Near the top of your file do something similar to this:
function _cb() {
console.log(arguments)
}
var repl = require("repl");
var context = repl.start("$ ").context;
context.cb = _cb;
Now just add to the context throughout your code. The _cb is a dummy callback to play with function calls that require one (and see what they'll return).
Seems like the REPL API has changed quite a bit, this code works for me:
var replServer = repl.start({
prompt: "node > ",
input: process.stdin,
output: process.stdout,
useGlobal: true
});
replServer.on('exit', function() {
console.log("REPL DONE");
});
You can also take a look at this answer https://stackoverflow.com/a/27536499/1936097. This code will automatically load a REPL if the file is run directly from node AND add all your declared methods and variables to the context automatically.
I am trying out node and it's Express framework via the Express boilerplate installation. It took me a while to figure out I need Redis installed (btw, if you're making a boilerplate either include all required software with it or warn about the requirement for certain software - Redis was never mentioned as required) and to get my way around the server.js file.
Right now I'm still a stranger to how I could build a site in this..
There is one problem that bugs me specifically - when I run the server.js file, it says it's all good. When I try to access it in the browser, it says 'transferring data from localhost' and never ends - it's like render doesn't finish sending and never sends the headers. No errors, no logs, no nothing - res.render('index') just hangs. The file exists, and the script finds it, but nothing ever happens. I don't have a callback in the render defined, so headers should get sent as usual.
If on the other hand I replace the render command with a simple write('Hello world'); and then do a res.end();, it works like a charm.
What am I doing wrong with rendering? I haven't changed a thing from the original installation btw. The file in question is index.ejs, it's in views/, and I even called app.register('.ejs', require('ejs')); just in case before the render itself. EJS is installed.
Also worth noting - if I do a res.render('index'); and then res.write('Hello'); immediately afterwards, followed by res.end();, I do get "Hello" on the screen, but the render never happens - it just hangs and says "Transferring data from localhost". So the application doesn't really die or hang, it just never finishes the render.
Edit: Interesting turn of events: if I define a callback in the render, the response does end. There is no more "Transferring data...", but the view is never rendered, neither is the layout. The source is completely empty upon inspection. There are no errors whatsoever, and no exceptions.
Problem fixed. It turns our render() has to be the absolute last command in a routing chain. Putting res.write('Hello'); and res.end(); after it was exactly what broke it.
I deleted everything and wrote simply res.render('index') and it worked like a charm. Learn from my fail, newbies - no outputting anything after rendering!
Did anyone set up something like this for himself using the existing
node.js REPL? I didn't think of a quick way to do it.
The way I do it today is using emacs and this:
https://github.com/ivan4th/swank-js
This module is composed of:
A SLIME-js addon to emacs which, in combination with js2-mode, lets
you simply issue a C-M-x somewhere in the body of a function def - and
off goes the function's string to the ..
Swank-js server (yes, you could eval from your local-machine
directly to a remote process) written in Node.js - It receives the
string of the function you eval'ed and actually evals it
A whole part that lets you connect to another port on that server
with your BROWSER and then lets you manipulate the DOM on that browser
(which is pretty amazing but not relevant)
My solution uses SLIME-js on the emacs side AND I require('swank-
js') on my app.js file
Now.. I have several issues and questions regarding my solution or
other possible ones:
Q1: Is this overdoing it? Does someone have a secret way to eval stuff
from nano into his live process?
Q2: I had to change the way swank-js is EVALing.. it used some
kind of black magic like this:
var Script = process.binding('evals').Script;
var evalcx = Script.runInContext;
....
this.context = Script.createContext();
for (var i in global) this.context[i] = global[i];
this.context.module = module;
this.context.require = require;
...
r = evalcx("CODECODE", this.context, "repl");
which, as far I understand, just copies the global variables to the
new context, and upon eval, doesn't change the original function
definitions - SOOO.. I am just using plain "eval" and IT
WORKS.
Do you have any comments regarding this?
Q3: In order to re-eval a function, it needs to be a GLOBAL function -
Is it bad practice to have all function definitions as global (clojure-like) ? Do you think there is another way to do this?
Actually, swank.js is getting much better, and it is now much easier to set up swank js with your project using NPM. I'm in the process of writing the documentation right now, but the functionality is there!
Check this out http://nodejs.org/api/vm.html
var util = require('util'),
vm = require('vm'),
sandbox = {
animal: 'cat',
count: 2
};
vm.runInNewContext('count += 1; name = "kitty"', sandbox, 'myfile.vm');
console.log(util.inspect(sandbox));
// { animal: 'cat', count: 3, name: 'kitty' }
Should help you a lot, all of the sandbox things for node uses it :) but you can use it directly :)
You might take a look at jsapp.us, which runs JS in a sandbox, and then exposes that to the world as a quick little test server. Here's the jsapp.us github repo.
Also, stop into #node.js and ask questions for a quicker response :)