The essence of influence is the output of spirit.

Antecedents to review

The previous article mainly shared a NodeJS module search mechanism, the search process roughly goes through path analysis, file location, compilation and execution of these three processes. Today we continue to talk about Node module parsing and NPM knowledge

Modular compilation

Each module in Node is an object, like this:

function module(id,parent){

  this.id = id;

  this.exports = {}

  this.parent = parent;

  if(parent && parent.children){

    parent.children.push(this)

  }

  this.filename = null;

  this.loaded = false;

  this.children = [];

}



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Once the file is located, Node creates a new module child object, which it loads and compiles according to the path. Of course, the loading method varies depending on the file type.

  • .js filethroughfsThe module is compiled after reading
  • The node fileIs written in C++ extension file, throughdlopen()Method loads the file generated by the last compilation
  • The json filethroughfsAfter reading, useJSON.parseParse and return the result

Node reads different types of files, such as json files:

// Native extion for .json



module._extentions['.json'] = function (module,filename) {

  var content = NativeModule.require('fs').readFileSync(filename,'utf-8')

  try{

    module.exports = JSON.parse(content)

  }catch(err){

    err.message = filename + ':' + err.message

    throw err;

  }

}



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How do JS modules compile?

Require,exports, and module exist in every JS file, but we didn’t define them. In the Node documentation, we can also find the __dirname and __filename variables. Where do they come from?

Node actually wraps the retrieved JS file. Added (function(exports,require,module,__filename,__dirname){in the header, added} in the tail). Such as:



  (function(exports,require,module,__filename,__dirname){

    var math = require('math')

    exports.add = function(a,b){

      return a+b

    }

  })

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This isolates each module file from each other. Meanwhile, the wrapped code is executed through the native module’s runInThisContext() method, which returns a concrete object. Finally, the current module object’s exports,module, require properties are passed to function() as arguments. This way, these variables are not defined, but they do exist in the module file.

NPM and package

We probably use NPM a lot and know it as a package manager, but most of us don’t give much thought to the details.

  • What is a bag?

    A package is actually an archive file, that is, a directory packaged directly as a.zip or.tar.gz format. Decompress the installation package to a directory. Conforming package directories should contain the following files

    • package.jsonPackage description file
    • binStore executable binaries
    • libStoring JS code
    • docdocumentation
    • testStore unit test case code

  • Package description file

Pageage. json is used to describe information that is not relevant to the specific code.

  • The name package name

  • The description package introduction

  • Version version number

  • Keywords keywords

  • Maintainers List of maintainers

  • List of Contributors

  • License License List

  • Respositories host source code address

  • Dependencies depend on the package

  • Homepage Homepage

  • OS List of supported operating systems

  • Cpucpu architecture support list

  • Engine Supports a list of JS engines

  • Whether Builtin is built into the standard components of the underlying system

  • Directories Specifies a package directory

  • Implements a list of implemented specifications

  • Scripts Script description object

  • Common functions of NPM

NPM is so common in everyday development that I won’t describe it too much. Here’s how to distribute a package. The following commands are used to publish a package:

  • NPM init Initializes the package

  • NPM adduser Adds a user

  • NPM publish upload package

If you want to see all the packages that can be found in the current path, you can execute NPM ls

conclusion

  • How do JS modules compile
  • NPM and package

One last word

  1. Move your rich little hands and “like it.”
  2. Move your rich little hands, “click here”
  3. All see here, might as well “add a follow”
  4. Might as well “forward”, good things to remember to share

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