Would it be possible to get an explanation of how npm start works?
I have an Angular 2 application written in Typescript. I enter npm start in the console and this both compiles and launches the application using Node's built in web server.
However what is the starting point for this? Which files does the npm start command read in order to compile and start the application? Also why do I use npm start and not e.g. node start? I understood that NPM was just the package manager for node itself.
What I understand so far:
I have a tsconfig.js file which tells the TypeScript compiler what to do.
I have a packages.json file which tells node which packages to download.
Where do the following files fit into this:
main.ts
app/app.module.ts - which I understand is the starting point for my application.
How do all of these components fit together to form the application?
npm start is just an alias for npm run start, which runs whatever command is in scripts.start in your package.json.
It neither knows nor cares about TypeScript, or Angular, or anything like that - it just executes whatever script it's given on the command line.
Related
I'm getting this output when trying to install a node application using npm install:
$ npm install
> ejs#2.7.4 postinstall /home/dh_8u42k7/quotegoodeair.com/node_modules/ejs
> node ./postinstall.js
/home/dh_8u42k7/quotegoodeair.com/node_modules/ejs/postinstall.js:9
let envDisable = isTrue(process.env.DISABLE_OPENCOLLECTIVE) || isTrue(process.
^^^
SyntaxError: Unexpected strict mode reserved word
I have already found this question which contains a workaround. However, this isn't my own code, so I can't just remove "let", it seems to be a problem with ejs itself.
For another thing, the file postinstall.js doesn't even exist, even the ejs folder doesn't exist, so I can't just go in and edit the file.
Is there something wrong with my node application, or with ejs, or maybe with npm or Node itself? Why does Node install components which aren't supported by Node? Why does Node tell me there's an error in a file which doesn't exist?
It may be that your version of node does not support the features in the application you are trying to install.
One solution may be to find out what the version of node the application that you are trying to install originally used.
I believe you can check the engine field in your package.json file.
If you local node version is different, and you need to change it, here is a link to a question providing that information: How can I specify the required Node.js version in package.json?
I also found this post interesting: https://github.com/tj/n/issues/472
It's for a different application but they received the same error message. The issue was conflicting npm folders. It's possible that the program that you are trying to install is conflicting with your existing npm setup if you have other nom folders in the directory you are installing the application in.
Ultimately, given the information you provided, I think your best bet it to look in the package.json file of the application you're trying to install and see if your local setup is conflicting with how the program is trying to be installed or run.
So I have have been using NPM as a simple build tool for a few years where I can assume that every CLI tool installed through package.json is available in the PATH, as NPM adds the ./node_modules/.bin path to it.
But as I was about to write a small Node script to do some house cleanup chores I got a bit wary if NPM actually has the node executable in the PATH it gives to users. This might seems stupid, as all the scripts in ./node_modules/.bin rely on node being there for the wrapper scripts on Unix to be able to find it, but I thought there might be some magic going on in Windows. Perhaps they use some other magic of their own. Or something. Does not matter, really, I just want to be able to assert:
Is the node executable always on the PATH given to npm scripts by NPM? On all platforms? And is it always the same Node as NPM runs on?
This might seem too basic to almost be asked, but better safe than sorry.
Note: not a definitive answer, but too lengthy for a comment
If you look at the documentation on default values that are set up for scripts:
npm will default some script values based on package contents.
"start": "node server.js":
If there is a server.js file in the root of your package, then npm
will default the start command to node server.js.
Although this isn't a definitive answer to your question, npm uses node as a default in case there's no npm start defined. This is a clear indicator npm relies on node to be present under all circumstances.
On Windows, you can safely make the assumption that npm requires node to be in the PATH, or in the same folder as npm. This is from npm.cmd (the script that is called when you type npm):
SET "NODE_EXE=%~dp0\node.exe"
IF NOT EXIST "%NODE_EXE%" (
SET "NODE_EXE=node"
)
I'm familiar with debugging my own node apps (usually with node-inspector). Today I'd like to debug someone else's program. I'm trying to track down an issue with supervisor. So naturally I just add a --debug (or debug-brk) to the command call, but it passes that to the code that it is supervising.
I've tried adding debugger lines to the js file for supervisor but that didn't work (probably because no debugger was attached at that time). There's a bit of a race here -- I need to start the debugger and attach it to the supervisor process after it starts but before it processes its arguments from the command line.
What I really want to do here is stop supervisor and debug it before it processes its command line arguments. How can I do this?
I had the same problem while developing my hexo blog. The documentation isn't all that complete yet so I find myself needing to reverse engineer at times.
The basic idea is that in Node.js even your cli apps are simply normal node apps that you are exposing to the OS command line interface. On Unix systems you are using this line:
#!/usr/bin/env node
To allow the environment to execute the script.
Many cli based node apps try to insist that you install them globally with the -g option.
npm install -g node-inspector
I personally prefer to have as much control of my development environment as I can get, so I prefer to break some conventions and check my node_modules in to source control along with installing everything I can locally by dropping the -g.
npm install node-inspector
Now you don't have to do this in order to make this work, I'm just describing this setup because it relates to your question. When I run node-inspector I can't simply use:
node-inspector
Instead I must explicitly invoke it from within my project. I do this by executing the symlink in my node_modules/.bin folder:
node_modules/.bin/node-inspector
Now I'm running node-inspector just like you.
Next all I need to do is start the cli process in debug and optionally pass params to it:
node --debug-brk node_modules/.bin/hexo generate
Note I am explicitly calling the symlink here and not simply:
node --debug-brk hexo generate
If I tried the line above I would get an error: "Error: Cannot find module".
I hope this helps.
I am new to node. I am trying to run an express server. I get no errors when installing express but when i run npm start or node app (as all the beginner tutorials point) nothing seems to be happening. The only way i can start the server is by typing node /bin/www. My operating system is Windows. Any advice?
The Express scaffold script generates a package.json file with a start script field that points to the app.js file it also created. Since Express 4 was released the scaffold generator script has been moved to its own package. https://github.com/expressjs/generator
All npm start does is look in the package.json file for a starting script to pass to node. You can see this in the documentation.
Running npm start with a package.json like this:
"scripts": {
"start": "app.js"
}
Is exactly equivalent to running node app.js.
I managed to solve my issue by changing the code page of cmd-dos. By using chcp 850 or chcp 65001 in cmd thus changing codepage to latin - utf8 the issue is gone.
I was thinking it would be handy if I could reload! code in the Node console, something to the effect of:
reload('./path/to/my/file.js')
that would delete the code from the cache then load it again -- handy for exercising prototype code. Seemed like a natural function to place in node's equivalent of ~/.irbrc. But I can't find that. Does node have such a thing?
I don't know there's such a tool. But I believe what you need can be achieved by using nodemon.
Use sudo npm install nodemon -g to install it. Then launch your application by nodemon app.js instead of node app.js. Then it watches for changes to nearby .js files, and automatically restart when you save.