How to use the main parameter in package json

Question

I have done quite some search already  However  still having doubts about the  main  parameter in the package json of a Node project   How would filling in this field help  Asking in another way  can I start the module in a different style if this field presents  Can I have more than one script filled into the main parameter  If yes  would they be started as two threads  If no  how can I start two scripts in a module and having them run in parallel   I know that the second question is quite weird  It is because I have hosted a Node js application on OpenShift but the application consists of two main components  One being a REST API and one being a notification delivering service  I am afraid that the notification delivering process would block the REST API if they were implemented as a single thread  However  they have to connect to the same MongoDB cartridge  Moreover  I would like to save one gear if both the components could be serving in the same gear if possible  Any suggestions are welcome

User · Answer

For OpenShift  you only get one PORT and IP pair to bind to  per application    It sounds like you should be able to serve both services from a single nodejs instance by adding internal routes for each service endpoint   I have some info on how OpenShift uses your project s package json to start your application here  https   www openshift com blogs run-your-nodejs-projects-on-openshift-in-two-simple-steps package json

User · Answer

As far as I know  it s the main entry point to your node package  library  for npm  It s needed if your npm project becomes a node package  library  which can be installed via npm by others   Let s say you have a library with a build   dist   or lib  folder  In this folder  you got the following compiled file for your library  -lib  --bundle js  Then in your package json  you tell npm how to access the library  node package        quot name quot    quot my-library-name quot      quot main quot    quot lib bundle js quot            After installing the node package with npm to your JS project  you can import functionalities from your bundled bundle js file  import   add  subtract   from  my-library-name     This holds also true when using Code Splitting  e g  Webpack  for your library  For instance  this webpack config js makes use of code splitting the project into multiple bundles instead of one  module exports       entry        main     src index js       add     src add js       subtract     src subtract js          output        path       dirname  lib       filename    name  js       library   my-library-name       libraryTarget   umd                 Still  you would define one main entry point to your library in your package json       quot name quot    quot my-library-name quot      quot main quot    quot lib main js quot            Then when using the library  you can import your files from your main entry point  import   add  subtract   from  my-library-name    However  you can also bypass the main entry point from the package json and import the code splitted bundles  import add from  my-library-name lib add   import subtract from  my-library-name lib subtract    After all  the main property in your package json only points to your main entry point file of your library

User · Answer

Just think of it as the  starting point     In a sense of object-oriented programming  say C   it s the init   or constructor of the object class  that s what  entry point  meant   For example  public class IamMain     when export and require this guy       public IamMain       this is  main                          many others such as function  properties  etc

User · Answer

From the npm documentation      The main field is a module ID that is the primary entry point to your   program  That is  if your package is named foo  and a user installs   it  and then does require  foo    then your main module s exports   object will be returned       This should be a module ID relative to the root of your package   folder       For most modules  it makes the most sense to have a main script and   often not much else    To put it short    You only need a main parameter in your package json if the entry point to your package differs from index js in its root folder  For example  people often put the entry point to lib index js or lib  lt packagename gt  js  in this case the corresponding script must be described as main in package json  You can t have two scripts as main  simply because the entry point require  yourpackagename   must be defined unambiguously

User · Answer

One important function of the main key is that it provides the path for your entry point   This is very helpful when working with nodemon   If you work with nodemon and you define the main key in your package json as let say  main      src server app js   then you can simply crank up the server with typing nodemon in the CLI with root as pwd instead of nodemon   src server app js

User · Answer

If you have for instance in your package json file      name    zig-zag    main    lib entry js           lib entry js will be the main entry point to your package    When calling  require  zig-zag      in node  lib entry js will be the actual file that is required

User · Answer

To answer your first question  the way you load a module is depending on the module entry point and the main parameter of the package json   Let s say you have the following file structure   my-npm-module  -- lib      -- module js  -- package json   Without main parameter in the package json  you have to load the module by giving the module entry point  require  my-npm-module lib module js     If you set the package json main parameter as follows  main    lib module js   you will be able to load the module this way  require  my-npm-module

[javascript] How to use the 'main' parameter in package.json?

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