"section fourth node. js modules and Packages"

Concept: Modules (module) and packages are the most important pillars of node. js. It is not possible to develop a program of a certain size using only one file, usually by splitting, assembling, and then combining the various functions. The module was formally created to achieve this, and in browser JavaScript, the split and composition of the script module is usually implemented using the HTML script tag, and node. JS provides the Require function to invoke the other modules, andmodules are file-based, the mechanism is very simple, the difference between modules and packages is transparent, so it is often not differentiated.          Module              1. What is a module                The        modules and files are one by one corresponding. A node. js file is a module that may be JavaScript code, JSON, or compiled C/s extensions.                      var http=require (' http '), where HTTP is a core module of node. js, gets the module through the Require function and then uses the object in it              2. Creating and Loading modules                    (1) Creating Modules                           node. JS provides exports and require two objects, where exports is the interface that the module exposes, require is used to obtain an interface for a module from the outside, that is, to get the exports object of the module                    through two JS files at the same level: Module.js and Getmodule.js implementations:　　　　　　

　　　　　　

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(2) A single load the above example is a bit like creating an object, but actually it is fundamentally different from the object becauserequire does not load modules repeatedly, that is, no matter how many times require is called, the module gets the same                       change ⑴ getmodule.js to getmodule2.js:  run result:   &nb sp;                (3) Cover exports                       sometimes we just want to encapsulate an object in a module, such as                       Define Module:singleobejct.js                      Introducing modules using:getsingleobject.js                       A. Tedious:exports.hello=hello;                         Introduction: Require ("./singleobject") .hello;                      b. Easy: module.exports=　　　　　　 Hello

　　　　　　

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                  Exports itself is just an ordinary empty object, {}, which is specifically used to declare interfaces          II, create packages             1. Package Concept           The         package is a deeper abstraction on the module, and node. JS's package is similar to a C/s library or a Java class library, which speaks of a separate function encapsulated for publishing, updating , management-dependent versioning. NPM has been developed to address the release and acquisition requirements of packages.            2. How to create a package                  COMMONJS specification package should have a feature:                          package.json must be in the top-level directory of the package                           binary files should be in the bin directory                          The  javascript code should be in the Lib directory                           documentation should be in the doc directory                            unit tests should be in the test directory                  node.js The package requirements are not so strict, as long as the top-level directory has Package.json, and conforms to the basic specifications can                       (1) Modules as folders                           Somepackage folder                           's simplest package is a module that acts as a folder,                          Create a folder Somepackage, There is a index.js inside, which provides a way to SayHello ()                          var Somepackage=require ('./somepackage ');                           somepackage.sayhello ();                          We use this method to encapsulate a folder into a module, the so-called package. A package is usually a collection of modules that provide a higher level of abstraction on the basis of a module, equivalent to a library of functions that provide fixed interfaces, and by customizing Package.json we can create more complex, more sophisticated, more compliant packages for publishing.　　　　　　  

　　　　　　

                      (2) package.json                      in the previous example, under the Somepackage folder, we created a Package.json file, content                           {                              ' main ': './lib/index.js '                           }                      When node. JS calls a package, it checks the main field of the Package.json file in the package as an interface module for the package, and if the Package.json or main field does not exist, it will look for index.js or index. Code as the interface for the package   Package.json:　　　　　　

　　　　　　

　　　　　　

Note the path and file format package.js:

　　　　　　

　　　　　　

                   The canonical properties of the   package.json:                         name: The name of the package must be unique                           description: Brief description of the package                          version: Version strings that conform to the semantic version recognition specification                           keywords: keyword data, typically used for search                          maintainers: Maintainer array, each element containing name, Email, web optional field    &Nbsp;                     contributors: The contributor array, in the same format as maintainers. The sitting of the package should be the first element of the contributor's data                          bugs: The address where the bug was submitted can be a URL or an email address                           licenses: The license array, each element to contain the type and URL fields                          repositories: Warehouse managed Address Array, Each element must contain type, URL, and path fields                          dependencies: A dependency of a package, an associative array consisting of the package name and version number.　　　　　　  ⑶ new Getpackage.js, running result:  

　　　　　　

"section fourth node. js modules and Packages"