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For example, consider a file named foo. On the first line, foo. Functions and objects are added to the root of a module by specifying additional properties on the special exports object. Variables local to the module will be private, because the module is wrapped in a function by Node. In this example, the variable PI is private to circle. When a file is run directly from Node. That means that it is possible to determine whether a file has been run directly by testing require.
For a file foo. The semantics of Node. Package manager programs such as dpkg , rpm , and npm will hopefully find it possible to build native packages from Node. Packages can depend on one another. In order to install package foo , it may be necessary to install a specific version of package bar.
The bar package may itself have dependencies, and in some cases, these may even collide or form cyclic dependencies. Thus, even if a cycle is encountered, or if there are dependency conflicts, every module will be able to get a version of its dependency that it can use.
In order to make modules available to the Node. To get the exact filename that will be loaded when require is called, use the require. Putting together all of the above, here is the high-level algorithm in pseudocode of what require. Modules are cached after the first time they are loaded. This means among other things that every call to require 'foo' will get exactly the same object returned, if it would resolve to the same file. Multiple calls to require 'foo' may not cause the module code to be executed multiple times.
This is an important feature. With it, "partially done" objects can be returned, thus allowing transitive dependencies to be loaded even when they would cause cycles.
Modules are cached based on their resolved filename. Additionally, on case-insensitive file systems or operating systems, different resolved filenames can point to the same file, but the cache will still treat them as different modules and will reload the file multiple times.
For example, require '. These modules are described in greater detail elsewhere in this documentation. The core modules are defined within Node. Core modules are always preferentially loaded if their identifier is passed to require. For instance, require 'http' will always return the built in HTTP module, even if there is a file by that name. When there are circular require calls, a module might not have finished executing when it is returned.
At that point, b. In order to prevent an infinite loop, an unfinished copy of the a. By the time main. The output of this program would thus be:. Careful planning is required to allow cyclic module dependencies to work correctly within an application. If the exact filename is not found, then Node. A required module prefixed with '. It is convenient to organize programs and libraries into self-contained directories, and then provide a single entry point to that library.
There are three ways in which a folder may be passed to require as an argument. The first is to create a package. If this was in a folder at. If the file specified by the 'main' entry of package. If there is no package. For example, if there was no package. If it is not found there, then it moves to the parent directory, and so on, until the root of the file system is reached.
It is possible to require specific files or sub modules distributed with a module by including a path suffix after the module name. The suffixed path follows the same module resolution semantics. These will be loaded faster, and more reliably. Before a module's code is executed, Node. The directory name of the current module. This is the same as the path. The file name of the current module. This is the resolved absolute path of the current module file.
A reference to the module. See the section about the exports shortcut for details on when to use exports and when to use module. A reference to the current module, see the section about the module object. Modules are cached in this object when they are required.
By deleting a key value from this object, the next require will reload the module. Note that this does not apply to native addons , for which reloading will result in an Error.
See "Accessing the main module". Use the internal require machinery to look up the location of a module, but rather than loading the module, just return the resolved filename. Returns an array containing the paths searched during resolution of request or null if the request string references a core module, for example http or fs.
In each module, the module free variable is a reference to the object representing the current module. Sometimes this is not acceptable; many want their module to be an instance of some class. To do this, assign the desired export object to module. Note that assigning the desired object to exports will simply rebind the local exports variable, which is probably not what is desired. Note that assignment to module.
It cannot be done in any callbacks. This does not work:. The exports variable is available within a module's file-level scope, and is assigned the value of module. It allows a shortcut, so that module. However, be aware that like any variable, if a new value is assigned to exports , it is no longer bound to module. To illustrate the behavior, imagine this hypothetical implementation of require , which is quite similar to what is actually done by require:.
In order to do this, it is necessary to get a reference to the module object. Since require returns the module. Provides general utility methods when interacting with instances of Module — the module variable often seen in file modules.
Accessed via require 'module'. A list of the names of all modules provided by Node. Can be used to verify if a module is maintained by a third party or not. Note that module in this context isn't the same object that's provided by the module wrapper. To access it, require the Module module:. Table of Contents Modules Accessing the main module Addenda: Package Manager Tips All Together History Version Changes v8.