Node.js Manual & Documentation

Table Of Contents

Modules 模块

Node uses the CommonJS module system. Node has a simple module loading system. In Node, files and modules are in one-to-one correspondence. As an example, foo.js loads the module circle.js in the same directory.

Node使用CommonJS模块系统。Node有一个简单的模块装载系统，在Node中，文件和模块是一一对应的。下面的例子展示了foo.js文件如何在相同的目录中加载circle.js模块。

The contents of foo.js:

foo.js的内容为：

var circle = require('./circle.js');
console.log( 'The area of a circle of radius 4 is '
           + circle.area(4));

The contents of circle.js:

circle.js的内容为：

var PI = Math.PI;

exports.area = function (r) {
  return PI * r * r;
};

exports.circumference = function (r) {
  return 2 * PI * r;
};

The module circle.js has exported the functions area() and circumference(). To export an object, add to the special exports object.

circle.js模块输出了area()和circumference()两个函数，为了以对象的形式输出，需将要输出的函数加入到一个特殊的exports对像中。

Variables local to the module will be private. In this example the variable PI is private to circle.js.

模块的本地变量是私有的。在上面的例子中，变量PI就是circle.js私有的。

Core Modules 核心模块

Node has several modules compiled into the binary. These modules are described in greater detail elsewhere in this documentation.

Node有一些编译成二进制的模块。这些模块在这篇文档的其他地方有详细描述。

The core modules are defined in node's source in the lib/ folder.

核心模块在node源代码中的lib文件夹下。

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.

核心模块总是被优先加载，如果它们的标识符被require()调用。例如，require('http')将总是返回内建的HTTP模块，即便又一个同名文件存在。

File Modules 文件模块

If the exact filename is not found, then node will attempt to load the required filename with the added extension of .js, and then .node. .js files are interpreted as JavaScript text files, and .node files are interpreted as compiled addon modules loaded with dlopen.

如果没有找到确切的文件名，node将尝试以追加扩展名.js后的文件名读取文件，如果还是没有找到则尝试追加扩展名.node。.js文件被解释为JavaScript格式的纯文本文件，.node文件被解释为编译后的addon（插件）模块，并使用dlopen来加载。

A module prefixed with '/' is an absolute path to the file. For example, require('/home/marco/foo.js') will load the file at /home/marco/foo.js.

以'/'为前缀的模块是一个指向文件的绝对路径，例如require('/home/marco/foo.js')将加载文件/home/marco/foo.js。

A module prefixed with './' is relative to the file calling require(). That is, circle.js must be in the same directory as foo.js for require('./circle') to find it.

以'./'为前缀的模块是指向文件的相对路径，相对于调用require()的文件。也就是说为了使require('./circle') 能找到正确的文件，circle.js必须位于与foo.js 相同的路径之下。

Without a leading '/' or './' to indicate a file, the module is either a "core module" or is loaded from a node_modules folder.

如果标明一个文件时没有 '/' 或 './'前缀，该模块或是"核心模块"，或者位于 node_modules目录中。

Loading from `node_modules` Folders 从 `node_modules` 目录中加载

If the module identifier passed to require() is not a native module, and does not begin with '/', '../', or './', then node starts at the parent directory of the current module, and adds /node_modules, and attempts to load the module from that location.

如果传递到 require()的模块标识符不是一个核心模块，并且不是以'/'，'../'或'./'开头，node将从当前模块的父目录开始，在其/node_modules子目录中加载该模块。

If it is not found there, then it moves to the parent directory, and so on, until either the module is found, or the root of the tree is reached.

如果在那里没有找到，就转移到上一级目录，依此类推，直到找到该模块或到达目录树的根结点。

For example, if the file at '/home/ry/projects/foo.js' called require('bar.js'), then node would look in the following locations, in this order:

例如，如果在文件 '/home/ry/projects/foo.js'中调用 `require('bar.js')，node将会依次查找以下位置：

This allows programs to localize their dependencies, so that they do not clash.

这允许程序本地化他们的依赖关系，避免发生冲突。

Optimizations to the `node_modules` Lookup Process 优化 `node_modules` 的查找过程

When there are many levels of nested dependencies, it is possible for these file trees to get fairly long. The following optimizations are thus made to the process.

如果有很多级的嵌套信赖，文件树会变得相当的长，下面是对这一过程的一些优化。

First, /node_modules is never appended to a folder already ending in /node_modules.

首先， /node_modules不要添加到以 /node_modules结尾的目录上。

Second, if the file calling require() is already inside a node_modules hierarchy, then the top-most node_modules folder is treated as the root of the search tree.

其次，如果调用require()的文件已经位于一个node_modules层次中，最上级的node_modules目录将被作为搜索的根。

For example, if the file at '/home/ry/projects/foo/node_modules/bar/node_modules/baz/quux.js' called require('asdf.js'), then node would search the following locations:

例如，如果文件'/home/ry/projects/foo/node_modules/bar/node_modules/baz/quux.js'调用require('asdf.js')，node会在下面的位置进行搜索：

Folders as Modules 目录作为模块

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.

很方便将程序或库组织成自包含的目录，并提供一个单独的入口指向那个库。有三种方式可以将一个子目录作为参数传递给 require() 。

The first is to create a package.json file in the root of the folder, which specifies a main module. An example package.json file might look like this:

第一种方法是在目录的根下创建一个名为package.json的文件，它指定了一个main 模块。一个package.jso文件的例子如下面所示：

{ "name" : "some-library",
  "main" : "./lib/some-library.js" }

If this was in a folder at ./some-library, then require('./some-library') would attempt to load ./some-library/lib/some-library.js.

如果此文件位于./some-library目录中，require('./some-library')将试图加载文件./some-library/lib/some-library.js。

This is the extent of Node's awareness of package.json files.

这是Node感知package.json文件的范围。

If there is no package.json file present in the directory, then node will attempt to load an index.js or index.node file out of that directory. For example, if there was no package.json file in the above example, then require('./some-library') would attempt to load:

如果在目录中没有package.json文件，node将试图在该目录中加载index.js 或 index.node文件。例如，在上面的例子中没有 package.json文件，require('./some-library')将试图加载：

Caching 缓存

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.

模块在第一次加载后将被缓存。这意味着（类似其他缓存）每次调用require('foo')如果解析到相同的文件，那么将返回同一个对象。

All Together... 总结一下...

To get the exact filename that will be loaded when require() is called, use the require.resolve() function.

可使用require.resolve()函数，获得调用require()时将加载的准确的文件名。

Putting together all of the above, here is the high-level algorithm in pseudocode of what require.resolve does:

综上所述，这里以伪代码的形式给出require.resolve的算法逻辑：

require(X)
1. If X is a core module,
   a. return the core module
   b. STOP
2. If X begins with `./` or `/`,
   a. LOAD_AS_FILE(Y + X)
   b. LOAD_AS_DIRECTORY(Y + X)
3. LOAD_NODE_MODULES(X, dirname(Y))
4. THROW "not found"

LOAD_AS_FILE(X)
1. If X is a file, load X as JavaScript text.  STOP
2. If X.js is a file, load X.js as JavaScript text.  STOP
3. If X.node is a file, load X.node as binary addon.  STOP

LOAD_AS_DIRECTORY(X)
1. If X/package.json is a file,
   a. Parse X/package.json, and look for "main" field.
   b. let M = X + (json main field)
   c. LOAD_AS_FILE(M)
2. LOAD_AS_FILE(X/index)

LOAD_NODE_MODULES(X, START)
1. let DIRS=NODE_MODULES_PATHS(START)
2. for each DIR in DIRS:
   a. LOAD_AS_FILE(DIR/X)
   b. LOAD_AS_DIRECTORY(DIR/X)

NODE_MODULES_PATHS(START)
1. let PARTS = path split(START)
2. let ROOT = index of first instance of "node_modules" in PARTS, or 0
3. let I = count of PARTS - 1
4. let DIRS = []
5. while I > ROOT,
   a. if PARTS[I] = "node_modules" CONTINUE
   c. DIR = path join(PARTS[0 .. I] + "node_modules")
   b. DIRS = DIRS + DIR
6. return DIRS

Loading from the `require.paths` Folders 从`require.paths`目录中加载

In node, require.paths is an array of strings that represent paths to be searched for modules when they are not prefixed with '/', './', or '../'. For example, if require.paths were set to:

在node中，require.paths是一个保存模块搜索路径的字符串数组。当模块不以'/'，'./'或'../'为前缀时，将从此数组中的路径里进行搜索。例如，如果require.paths如下设置：

[ '/home/micheil/.node_modules',
  '/usr/local/lib/node_modules' ]

Then calling require('bar/baz.js') would search the following locations:

当调用require('bar/baz.js')时将搜索下列位置：

The require.paths array can be mutated at run time to alter this behavior.

可以在运行时改变require.paths数组的内容，以改变路径搜索行为。

It is set initially from the NODE_PATH environment variable, which is a colon-delimited list of absolute paths. In the previous example, the NODE_PATH environment variable might have been set to:

此数组使用NODE_PATH环境变量进行初始化，此环境变量是冒号分割的路径列表。在之前的例子中，NODE_PATH环境变量被设置为如下内容：

/home/micheil/.node_modules:/usr/local/lib/node_modules

Loading from the require.paths locations is only performed if the module could not be found using the node_modules algorithm above. Global modules are lower priority than bundled dependencies.

只有当使用上面介绍的node_modules算法无法找到模块时，才会从require.paths地址里进行加载。全局模块比绑定抵赖的模块优先级低。

**Note:** Please Avoid Modifying `require.paths` **注意：** 请不要修改`requires.paths`

For compatibility reasons, require.paths is still given first priority in the module lookup process. However, it may disappear in a future release.

由于兼容性的原因，require.paths仍然在模块查询过程中处于第一优先级。然而，在未来发布的版本中这个问题将被解决。

While it seemed like a good idea at the time, and enabled a lot of useful experimentation, in practice a mutable require.paths list is often a troublesome source of confusion and headaches.

虽然在当时看起来这是个好注意，可以支持很多有用的实验手段。但在实践中发现，修改require.paths列表往往是造成混乱和麻烦的源头。

Setting `require.paths` to some other value does nothing. 将`require.paths`设为其他值不会产生任何作用

This does not do what one might expect:

下述做法不会其他你期望的任何效果：

require.paths = [ '/usr/lib/node' ];

All that does is lose the reference to the actual node module lookup paths, and create a new reference to some other thing that isn't used for anything.

这么做将会丢失对真正的模块搜索路径列表对象的引用，同时指向了一个新创建的对象，而这个对象将不会其任何作用。

Putting relative paths in `require.paths` is... weird. 不建议在`require.paths`中发入相对路径

If you do this:

如果你这样做：

require.paths.push('./lib');

then it does not add the full resolved path to where ./lib is on the filesystem. Instead, it literally adds './lib', meaning that if you do require('y.js') in /a/b/x.js, then it'll look in /a/b/lib/y.js. If you then did require('y.js') in /l/m/n/o/p.js, then it'd look in /l/m/n/o/lib/y.js.

这样只会添加'./lib'字符串到搜索路径列表，而不会解析./lib在文件系统中的绝对路径。这意味着如果你在/a/b/x.js中调用require('y.js')，将找到/a/b/lib/y.js。而如果你在/l/m/n/o/p.js中调用require('y.js')，将找到/l/m/n/o/lib/y.js。

In practice, people have used this as an ad hoc way to bundle dependencies, but this technique is brittle.

在实践中，有用户使用这种特别的方式来实现绑定依赖，但这种方式是很脆弱的。

Zero Isolation 零隔离

There is (by regrettable design), only one require.paths array used by all modules.

由于设计的失误，所有模块都共享同一个require.paths数组。

As a result, if one node program comes to rely on this behavior, it may permanently and subtly alter the behavior of all other node programs in the same process. As the application stack grows, we tend to assemble functionality, and it is a problem with those parts interact in ways that are difficult to predict.

造成的结果是，如果一个node程序依赖于这种行为，它将永久的并且隐蔽的改变处在同个进程内的所有其他node程序的行为。一旦应用程序变大，我们往往进行功能集成，各部分功能以不可预料的方式互相影响将成为问题。

Addenda: Package Manager Tips 附录：包管理技巧

The semantics of Node's require() function were designed to be general enough to support a number of sane directory structures. Package manager programs such as dpkg, rpm, and npm will hopefully find it possible to build native packages from Node modules without modification.

Node的require()函数的语义被设计的足够通用化，以支持各种常规目录结构。包管理程序如 dpkg，rpm和npm将不用修改就能够从Node模块构建本地包。

Below we give a suggested directory structure that could work:

接下来我们将给你一个可行的目录结构建议：

Let's say that we wanted to have the folder at /usr/lib/node/<some-package>/<some-version> hold the contents of a specific version of a package.

假设我们希望将一个包的指定版本放在/usr/lib/node/<some-package>/<some-version>目录中。

Packages can depend on one another. In order to install package foo, you may have to install a specific version of package bar. The bar package may itself have dependencies, and in some cases, these dependencies may even collide or form cycles.

包可以依赖于其他包。为了安装包foo，可能需要安装包bar的一个指定版本。包bar也可能有依赖关系，在一些情况下依赖关系可能发生冲突或形成循环。

Since Node looks up the realpath of any modules it loads (that is, resolves symlinks), and then looks for their dependencies in the node_modules folders as described above, this situation is very simple to resolve with the following architecture:

因为Node会查找它所加载的模块的真实路径（也就是说会解析符号链接），然后按照上文描述的方式在node_modules目录中寻找依赖关系，所以可以使用如下的目录结构解决这个问题：

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.

因此即便存在循环依赖或依赖冲突，每个模块还是可以获得他所依赖的包的一个可用版本。

When the code in the foo package does require('bar'), it will get the version that is symlinked into /usr/lib/node/foo/1.2.3/node_modules/bar. Then, when the code in the bar package calls require('quux'), it'll get the version that is symlinked into /usr/lib/node/bar/4.3.2/node_modules/quux.

当包foo中的代码调用require('bar')，将获得符号链接/usr/lib/node/foo/1.2.3/node_modules/bar指向的版本。同样，当包bar中的代码调用require('queue')，降火的符号链接/usr/lib/node/bar/4.3.2/node_modules/quux指向的版本。

Furthermore, to make the module lookup process even more optimal, rather than putting packages directly in /usr/lib/node, we could put them in /usr/lib/node_modules/<name>/<version>. Then node will not bother looking for missing dependencies in /usr/node_modules or /node_modules.

为了进一步优化模块搜索过程，不要将包直接放在/usr/lib/node目录中，而是将它们放在/usr/lib/node_modules/<name>/<version>目录中。这样在依赖的包找不到的情况下，就不会一直寻找到/usr/node_modules目录或/node_modules目录中了。

In order to make modules available to the node REPL, it might be useful to also add the /usr/lib/node_modules folder to the $NODE_PATH environment variable. Since the module lookups using node_modules folders are all relative, and based on the real path of the files making the calls to require(), the packages themselves can be anywhere.

为了使模块在node REPL中可用，你可能需要将/usr/lib/node_modules目录加入到$NODE_PATH环境变量中。由于在node_modules目录中搜索模块使用的是相对路径，基于调用require()的文件所在真实路径，因此包本身可以放在任何位置。